I agree with warrensaged here. In my case, I get a headache from spice only when there are either outside influences or an especially visually intense experience (such as an open eye experience).
If I have coffee or any sort of caffeine before a spice journey, likely to have a headache. Now, caffeine can have *similar* effects on the body as adrenaline. Thinking about the cold, moist palms, increased breathing, and jitters of before and after taking spice. This is your body going into fight or flight mode, very normal considering your body knows what is about to enter in and you have nothing to tell your mind about what to expect. This means constriction of non-necessary veins, increased hear rate, and most importantly increased blood pressure. Increased blood pressure is one of the top causes for headaches. That noggin is a sensitive place! A little swelling in any area of the brain due to dehydration or high blood pressure and you've got a headache, or worse, a migraine. Even after calming down to normal BP, your head can still be throbbing away. It happens.
The best ways I have found to prevent this? One, I try not to do spice after a rough work day. No matter how tempting it is, my body chemistry simply isn't ready for it. Two, drink plenty of water. We're made of the stuff, you'd be surprised what water could do for a headache. Make sure your cardiovascular health is in check, frequent walks and the occasional jog can help a lot with both stress relief and making sure your body can handle your mind going around the universe for a jog.
Last but not least, anything used in smoking the good stuff is clean and that there is zero chance of anything nasty mixing in. Once I got a big inhale of some super dirty lighter fluid smoke.. that was a headache/cough to remember. See just how much black smoke comes off the lighter flame. Some companies really skimp on the quality of the fluid.
If I missed/messed anything, anyone correct me!
EDIT: Ignore any use of "You, Your," this was addressed to SWIY.