How many times had you done shrooms before? I've only done em three times, never had a truly bad trip, as in like a panic attack type trip, but my experience has always been that shrooms make everything seem huge, intense, confusing and overwhelming. Combine that with other drugs that you have not combined before, and you've got potential for bad stuff to happen. Also, those must have been really potent shrooms if you only had half an eighth and still tripped hard. Or maybe the mushies in my town just suck. who knows. That would be my guess, anyway.