Heh well, the chances of a bad trip on (nearly) pure crystal MDMA are pretty slim, if not nonexistant. There can be some physical discomfort associated with using MDMA (hypertension, accelerated heartbeat, bruxia - teethgrinding -, increased sweating) but this will probably not bother you very much at all due to the overwhelming sense of euphoria.
Hell, on my first MDMA trip I suddenly felt very sure I was going to faint and maybe die (or at least that's how it felt at the time) but I was completely at peace with that. Dying there right on the spot would have been fine with me, that's how glorious and divine it was for me.
Instead of being afraid you might feel bad, you should probably worry about feeling too good. Once you've experienced total bliss you'll probably want to go there again and again - which is where the trouble starts.
Also, inappropriate bonding has been known to occur. Though most people are favorably inclined if you approach them which a big smile and open arms - some might feel threatened.. or you could wake up with the wrong person beside you in the morning.
Still, your mental faculties are more or less completely intact when using MDMA, so I wouldn't worry too much.
As to your weed brownie experience: many people make this mistake, unfortunately. They think smoking weed and eating a baked product containing THC (which means all the psychoactive compounds have bound themselves to fat molecules) does more or less the same thing. But the effects are very different, almost incomparable: you're much less in control, and you're forced to feel that way for at least a few hours. I think it's this fact in particular which is threatening to people high on weed brownies or hash cake.
Still, the most important thing is to realize your experience is always dependant on three factors: you (your mind/body), the substance used (effects vary in different batches, differnts means of production, different dosage) and the setting (involving everything from your friends to the music playing in the background. Your mileage can (and will) always vary. The experiences from the past (especially the nasty ones) will only resurface when you are anxious and start thinking of them again, trying to avoid 'going back there'. But when you do, it's best to just accept the feeling and then allow yourself to go on - instead of fighting it.
Hallucinogen Persisting Perception Disorder (HPPD) is veyr rare, and usually, if you're able to have a good experience using the same substance it will be associated with different emotional states, and the fear will be gone.
love
