For someone who has an anxiety disorder, there's a chance they may also have depression. And vice versa. "The symptoms of anxiety and depression actually have significant overlap," says Klapow. "Irritability, agitation, and feeling hopeless are common in both conditions."

But it's also the very nature of anxiety that can lead to depressive symptoms. "Very often anxiety disorders can become so disruptive on a person's life that they feel there is no hope of feeling better, and it's this feeling of hopelessness that can lead to co-occurring depression," Klapow says.

The good new is that, once managed, a person with anxiety and/or depression can certainly feel better. Trying certain lifestyle changes, such as getting more sleep, or meditating, can sometimes speed the process along, but it's also often a good idea to reach out to a therapist for support as well, especially if you're feeling too low to go it alone.

Post traumatic stress disorder, or PTSD, is a condition that often has depression as a side effect, and thus the two often go hand-in-hand. "Post traumatic stress disorder can be a highly disruptive disorder," Klapow says. "It causes intrusive thoughts, a hyper-startle response, sleep problems, and emotional numbing — all of which can cause significant debilitation."

This, in turn, can sometimes lead to depressive symptoms. "Often the source of the trauma can be a source of prolonged distress," Klapow adds. "The feeling of not being able to control these symptoms often leads to feelings of helplessness, which in turn can cause the person to 'give up' and lead to depression."

While a traumatizing or life-altering situation may have occurred — causing anxiety, depression, and flashbacks — there are ways to move past it, either with therapy, medication, or a combination of the two.

Obsessive Compulsive Disorder (OCD) is a type of anxiety disorder in and of itself. But it can also crop up with other types of anxiety, such as generalized anxiety disorder.

"OCD is a subset of most anxiety disorders," Donald Grothoff, a family OCD coach, tells Bustle. "OCD finds its way into anxiety as anxiety grows because I believe a person naturally wants to stop the anxiety and so they begin behaviors to stop it. Slowly that builds on its own. The mind begins looping messages and they grow stronger." And other anxieties result, which can manifest as compulsions. If you are finding that anxiety or OCD is making your day-to-day more difficult, reaching out to loved ones or consulting with a therapist can be a great way to learn how to cope.

For PTSD, the "the symptoms can be so distressing that often people use substances, like alcohol, to reduce their symptoms," says Klapow. "Over time the cycling of reducing the intrusive thoughts, helping reduce sleep problems, and trying to feel engaged can lead to a variety of substances being used." Someone with PTSD might, for example, not be able to get through the day without drinking.

And this can sometimes lead to substance use disorder. "Substance use disorder is basically the use of substances (everything from nicotine to heroin) that interferes with daily functioning, creates problems in work and relationships, etc.," says Klapow. "It's a psychiatric condition because of its negative impact on a person's life."

For someone who's struggling with PTSD or depression and using substances to feel better, reaching out to friends or a therapist is always a good idea. They can assist you in getting the help you need, so you can deal with trauma in a healthier way. Or if you prefer, calling the American Addiction Centers hotline, or the Substance Abuse and Mental Health Services Administration National Helpline can also help you find the care you need.

Schizophrenia and substance dependence often occur at the same time as well, for many of the same reasons. "A schizophrenic mind — which is always racing — uses alcohol to slow down the electrical processes of the brain," Caleb Backe, a health and wellness expert at Maple Holistics, tells Bustle. "[Alcohol] can be highly addictive, and has potential to damage vital organs. Alcohol use disorder (AUD) is one which schizophrenics are most likely to pick up as a co-occurring disorder."

If you or someone you know struggles with schizophrenia or substance abuse, there is no need to suffer alone. Speaking with loved ones, a therapist, or to a substance abuse helpline can offer information and resources to better manage symptoms.

While insomnia isn't a mental illness, sleep problems are often connected with mental health issues, such as depression and anxiety. And, since a lack of sleep can make conditions like these worse, it's definitely worth noting.

"Troubled sleep, or the inability to fall asleep, may be cause for major depression," says Backe. "Conversely, depression is a cause for insomnia and other sleep-related issues. It is a chicken and egg thing sometimes. Both disorders feed off each other, and a proper diagnosis is necessary to know how to approach the subject matter and the patient."

If you are finding that depression is affecting your sleep, or vice versa, talking to a therapist or someone you trust can be the first step to combatting this cycle.

Due to the symptoms of borderline personality disorder (BPD), which often can lead to problems with relationships, people with BPD can find themselves feeling isolated as a result, and that can lead to depressive symptoms, licensed marriage and family therapist Dr. Racine Henry, PhD, LMFT tells Bustle.

"BPD and depression can be comorbid because people with BPD often find themselves isolated from friends and loved ones and are ill-equipped to maintain a long term bond with others," she says. And for someone with BPD, that can make their situation feel even worse.

But it's important for people with BPD to keep in mind that their disorder is a condition that's treatable just like any other, and can be improved with things like dialectical behavioral therapy, which can teach them to better cope with emotions, and create healthier relationships.

BPD can also co-occur with other personality disorders, to a degree. "Personality disorders tend not to co-occur because the diagnosis of one usually rules out the diagnosis of another," Klapow says. But they can have symptoms that bleed over into one another.

"What you do see very often is a diagnosis of something like BPD with symptoms of histrionic personality disorder [a BPD categorized by attention seeking], but not the diagnosis," Klapow says. Therapists will often choose one diagnosis for their patients, but address all the symptoms present.

Eating disorders often co-occur with another mental health issues, such as depression or anxiety. "Eating disorders are genetic and circumstantial [illnesses], meaning that you have to have a genetic predisposition to develop an eating disorder, but genetics aren't typically enough," Stacey Rosenfeld, PhD, CGP, CEDS, of Gatewell Therapy Center, tells Bustle.

And, in some cases, it can be the co-occurring disorder that triggers them. "We know that coping with difficult emotions and mental illness, such as anxiety, depression, traumatic reactions, can be something that triggers eating disorder symptoms," she says. "Again, you have to have the underlying genetic disposition to start, but if that's the case, then coping with one of these other disorders can be difficult enough that eating disorder symptoms emerge (or intensify) as a way to manage the distress. It's also possible that some of the same biological/genetic factors that underly [eating disorders] also underly the other disorders."

And yet, as with other conditions, it's all treatable. Speaking with friends or loved ones, as well as talking with a therapist is a good place to start. Or, if this is something you are struggling with, calling the National Eating Disorder Association hotline can offer you resources on how to better cope, and seek help.

According to licensed psychologist Jennifer B. Rhodes, PsyD, attention deficit hyperactivity disorder (ADHD) can, for many people, co-occur with symptoms of anxiety.

"If ... the symptoms are severe enough to interfere with one’s personal goals, assessment and treatment can make these disorders much easier to manage," she says.

When someone has a mental health issue, it can help to know about the other mental health issues that can often go along with it. While it may feel overwhelming to have two or more issues occurring at the same time, there's always hope. A therapist or psychiatrist can help you figure out what exactly is going on, and decide on the proper treatment plan. There isn't anything that can't be managed with help, support, therapy, and/or medication.

If you or someone you know is facing issues with substance abuse, contact the American Addiction Center hotline at 888-455-9750 or the Substance Abuse and Mental Health Services Administration National Helpline at 1-800-662-HELP (4357) for additional resources.

If you or someone you know has an eating disorder and needs help, call the National Eating Disorders Association helpline at 1-800-931-2237, text 741741, or chat online with a Helpline volunteer here.