Stress

Anything that can cause mental stress needs to be dealt with. It doesn't matter if you think it's affecting you, since it definitely does. If you're worried about getting fired or maybe a bad grade, even if it's just at the back of your mind, that's definitely going to hurt your mentality in the long run.

If you just happen to be weak willed, you might eventually be crushed by the pressure to the point that you end up in an insane asylum. This naturally also depends on the amount of stress you're under. Otherwise you might start to notice your physical health constantly deteriorating. This can be due to a multitude of factors, some indirect and some direct. It has been proven that stress can lead to insomnia and lack of sleep will f*ck up your life more than just a bit.

By the time you notice something might be stressing you a bit more than you expected it'll already have become much harder to fix the problem. But as you, better late than never as in if you don't handle it correctly, you might never fully recover.