If you want symptoms, look for people having jelly legs if they're not experienced users, and also just conking out into kind of strange positions on chairs / the floor for long periods of time.

He's not about to run into the night screaming "THIS IS BAT COUNTRY" though, and the drug certainly isn't addictive, it doesn't have a high like a normal drug, you just feel totally altered (in my experience, acids really person dependent).

Wouldn't worry about it, infact, suggest you pop some with your friend some time, it might make you feel a bit closer to him since everything just pours out, and you seem a little uptight.