Probiotics. Effects and side-effects? [Gut health tied to brain function]

While reading about gut being tied to mental health and brain capability, I became interested in probiotics. I thought this was spot on since my gut havn't been feeling very well for a long time, and I havnt done anything about it.

I've been taking Jarrows EPS dophilus for a week but today I'm feeling really bad. Not in my stomach, which been working way better since I've started, but all around in my head. Feeling really shitty emotionally, like a big rock of depression which just hit me. Been really low today with a lot of negative thought patterns. Now I dont know if it could be the probiotics, but I dont take anything else except Theanine/Caffeine.

Anyone got experience of probiotics to share/or how gut health affected your mental health? Both positive and negative. And most important: anyone felt they got depressed from it?