Those stomach issues may actually be a result of what's going on in your head. "Patients with anxiety disorders can be presented with gastrointestinal upset such as nausea, abdominal pain, or even diarrhea," says Marra G. Ackerman, MD, Clinical Assistant Professor of Psychiatry, NYU Langone Medical Center, over email.

Drastic or concerning shifts in weight — whether it's weight loss or weight gain — can signify a mental health condition. "Eating disorders are a class of mental health disorders where a person has abnormal or inappropriate eating habits that most frequently leading to weight loss," says psychiatrist Dr. Ayo Gathing, MD over email. "Depression can also indirectly cause weight loss due to shifts in appetite with changes in mood."

People with bipolar disorder who are experiencing a manic episode may dress very colorfully or boldly or wear a lot make-up or jewelry, says Ackerman. "They can seem quite frenetic and highly energetic," she says. "Patients with psychotic disorders may also dress oddly for the weather, such as wearing a coat in the summer or in an otherwise odd fashion."

"Social withdrawal is often a sign of a serious mental issue," says clinical psychologist Dr. Carla Manly over email. "Those who suffer from certain mental health issues often worry that they will not be accepted, that they are 'inferior,' and that they must hide their disorder. As a result, they often retreat and self-isolate."

"Those who are severely depressed often have reduced energy, and therefore spend more time in sedentary, solitary activities," says Manly. Mental illness can cause fatigue for various reasons, ranging from affecting sleep patterns to lack of exercise to mental exhaustion.

People who suffer from depression often show a "blunted affect," which is a lack of facial expression. "The classic description is one of downcast eyes and slumped posture," says Dehorty. "This can vary, as people can 'brighten' their facial expressions and still feel depressed."

"Hygiene is often neglected when someone is in a depressive episode," says Dehorty. "Their hair may be unwashed and their clothes may be unkempt. They are just not that concerned with their physical appearance."

Anxiety can manifest itself in many physical ways, including tics. "There can be habitual movements such as rocking or other movements in an attempt to soothe," says Dehorty.

"It is fairly common for individuals with a mental health condition to complain of recurring aches and pains, hence the popular saying 'depression hurts,'" says Gathing. "It has been well documented that those with depression are three times more likely to develop chronic pain and report higher incidences of pain on physical exam."

The inability to rest or relax is a key indication that someone may be battling a mental health condition. "Not being able to sit still with constant moving or fidgeting can be present in attention deficit hyperactivity disorder (ADHD,) schizophrenia, or most commonly, in those with anxiety issues," says Gathing.

Although there is no single definition of a healthy sex drive, individuals with mental health issues often recognize a downward shift in their libido. "This decrease in sexual appetite can be related to the condition itself — such as with fatigue in depression — after a trauma in post traumatic stress disorder, or from body image issues in eating disorders," says Gathing.

Many people who suffer from mental illness often get frequent cold and infections, says psychologist Dr. Ganz Ferrance over email. "They won't heal as quickly at it won't go away as fast," he says. This can particularly happen when you're under a lot of stress.