Exactly my experience Ben, got rid of the initial attack pretty quickly but made the whole experience much worse. Generally the day after using Imitrex was a horror.

I use the Imitrix 4ml injection when I get attacks at night.  By the time I wake up, they are well under way   I also carry my injections with me when out and about (like walking the dog) and I can't get to my other abortives.  Otherwise, I chug energy drinks and inhale O2 which are also very effective when I can catch the hit early.  I have been known to inject myself 2-3x a day for a week before the prednisone and preventative du jour kicks in (I started with Verapamil but it became ineffective at 720 mg and I am now on Topamax 75mg) without ill effect.  I may be spacey but that is more due to the aftereffects of a hit than to the imitrix because I get that with any abortive. 

We are all sensitive biological organisms who respond differently to substances, even to substances that once worked for us!  For some, the rebound issue is not an issue.  I am one of those; these are the only headaches I get! 

It is always useful to find what works for you and what doesn't and to honor that.  Good luck!