You’ve been feeling awfully depressed for the past week when suddenly a wave of anxiety hits you.

At the same time, you start getting weird aches and pains in your stomach, back, and limbs. You might even get a headache and start to feel sluggish and fatigued.

Is it just bad luck, or are the two issues linked?

Contrary to popular belief, mental illness isn’t just “all in your head.” It affects your brain, yes, but because your brain affects the rest of your body, it’s no wonder that mental illness can make you feel ill.

So if you’re experiencing unexplained aches and pains, it might be linked to your mental health.

According to Carla Manley, PhD, a clinical psychologist and author, people with mental illnesses can experience a range of physical symptoms, such as muscle tension, pain, headaches, insomnia, and feelings of restlessness.

They might also experience “brain fog,” which is when your brain feels fuzzy and unfocused, and you may struggle to concentrate or remember information.

Anxiety can also cause stomach pain. For some, this might be just a flutter — like butterflies in your stomach. But it could also result in stomach pain or diarrhea, says Melissa Jones, PhD, a clinical psychologist.

“Many people get an upset stomach at times when they are nervous or trying something new. People with anxiety can have that feeling all of the time, and then have those symptoms increase to diarrhea or migraine when their anxiety and stressors increase,” Jones says.

When physical symptoms are caused or made worse by your mental state, it’s called psychosomatic.

Many people believe that psychosomatic symptoms aren’t real — but they are, in fact, very real symptoms that have a psychological cause, Jones says.

But why does mental stress cause physical illness? And what can you do about it?

How mental stress can cause physical problems

You might have heard of having a “fight or flight” response to danger. When we see danger, our bodies get ready to either fight the danger (fight) or run away (flight).

Our bodies become filled with two stress hormones: adrenaline and cortisol. This increases heart rate and blood pressure, suppresses the digestive system, and affects the immune system.

This is meant to help us exert a lot of physical energy, which we’d need if we were fighting or running away from danger. After the threat goes away, our bodies usually return to a resting state.

This is an evolutionary response that’s meant to keep you safe. It’s not necessarily a bad thing, as it helps you avoid or deal with danger.

“A certain level of anxiety known as ‘optimal anxiety’ can be very helpful in raising one’s motivation to an optimal level,” Manley explains. “In this way, anxiety — and the bit of stress it creates — provides the energy and interest required to complete many daily tasks.”

But if you’re in a constant state of stress or anxiety, it can wreak havoc on your body.

Constant stress means your cortisol and adrenaline levels will constantly be high and you’ll seldom return to a “resting” state. It can have a negative effect on your organs and bodily functions.

What’s more is that anxiety and depression may actually lower your pain tolerance.

The parts of the brain responsible for pain reception also relate to anxiety and depression, and the two neurotransmitters (serotonin and norepinephrine) that are responsible for pain signaling in the brain and nervous system are also implicated in anxiety and depression.

The symptoms of chronic stress include:

  • headaches
  • migraine
  • muscle tension and soreness
  • digestive issues such as diarrhea, stomach pain, and appetite changes
  • sleep issues or disorders
  • feelings of sluggishness

There are also a few physical symptoms of depression including:

Stress and trauma can also trigger autoimmune disorders like Hashimoto’s thyroiditis, psoriasis, rheumatic arthritis, and more.