Nightmares
I've been fighting on contract for 6 months. I'm not with ILDU, I'm with a Ukrainian unit. I just had my first "weekend" in 6 months, 3 days of rest in Dnipro city. The first night that I slept in a normal bed in a safe place, I had nightmares so bad I kept waking up drenched in sweat. I've never had nightmares in my life. I thought I was completely unaffected by the war - near the front, I sleep perfectly fine.
Just understand if you want to come fight, you will be affected psychologically, and it might not be apparent immediately.
Edit to add: don't get me wrong, I don't regret my choice to come and in fact I love fighting and I want more. My 6 month obligatory service is just about done, but I have no plans to break contract any time soon. This post wasn't to dissuade anyone who wants to come - just to be aware that you may not leave as the same person (if you leave at all).