It has been shown that temperature plays a very important role in the degree of neurotoxicity that MDMA can cause. This is just as relevant for cooler temps as it is for hotter. In other words, if the environmental temp. is varied from the considered optimum, your body will have great difficulty in regulating itself to approx. 37 deg., your normal body temp.
If you vomited it may have been induced by the shock of the change in temperature. Your body when shocked will often attempt to rid itself of the cause of the associated toxicity.
MDMA affects receptors in the hypothalamus, which causes a reversing affect of your body's normal temperature regulating mechanism. This special gland is also responsible for regulating visceral organs and their functions, e.g. stomach etc. and among many other things, it also coordinates neural and endocrine (glands) secretions and functions.
Once while DJing in Byron during August, I thought I would put on a long tune and zip out to the car for a jumper. I was rollin hard, and as I stepped out into the cold I broke out into an uncontrollable shiver, so much so I had to run back inside and get someone else to grab it. I've had it happen on a couple of other occasions since, and have seen others experience it as well.
Some have speculated too much E may affect your long term ability to regulate temperature, although I'm unaware of any research done into this.
Jessica Malberg, - Yale uni, did research on temp / mdma in rats. Here you'll find her work as presented at the Ecstasy conference
http://www.drugpolicy.org/ecstasy/conf_program.html
Anyone else experienced temp related problems when rollin'?
[Edit: fixed up paragraphing, p_d]