Think of it this way.
Say you gently poke your skin with a needle. You feel a slight pain. One that isn’t going to let up as long as the needle is there. But you could keep going if you had to. Though it would be hard.
The needle is mental illness.
Now imagine you were to take that same needle and jam it into your arm.
What’s your experience now?
The needle isn’t bigger, it’s still just a little bit. But wait!
In this case it’s under pressure. Stress placed upon a mind (already trending toward imbalance of some kind) can make whatever mental illness that is there far more vulnerable and reactive.
Please consider this when putting yourself or those you love in stressful situations.