Sometimes you can just have a bad trip on weed or at least thats happened to me. I remember once after smoking my stomach started hurting so fucking bad and I got real hot and started sweating and I thought that I had appendicitis and I felt like I was dying. Then I just told myself to calm down and that it was all in my head. And magically it all went away and I had a pleasant high for the rest of the night.

Oh I also got super pissed and kicked all my friends out of my house. (while i was in pain.) It's the only time i've ever gotten mad while high.