I couldn't wait to finally get Botox for the frown lines between my eyes. I had consulted my dermatologist months before, and finally got up the nerve to do it. After all, all of the websites I found when I searched "Botox" remarked about how absolutely safe it is, and how there are hundreds of thousands of these procedures every year.
The four injections I received were virtually painless. I could hardly believe how easy it was! I was already thinking maybe I will do more of this on the forehead lines one day. This was three days ago.
When I woke up the next morning, I had an EPIC HEADACHE, and bit of swelling over one of the injection sites. Thank God it's the weekend and I didn't have to drive my kids to school. Stomach upset set in, and the rest of the day was me sick in bed. Called the Dr. and he said we discussed that some get headaches, so take Tylenol and take it easy.
Now it is day two, and I am still on the Tylenol (I tried to go without it but the headache is fierce) and I feel like I have the flu. I have two children, and this is sooo NOT worth it. I think the safety and side effects of this are MINIMIZED by the PHARMACEUTICAL companies, in this case Allergan.
The truth is, there are those of us who will not tolerate this well, and unfortunately we don't know until after the procedure. I urge those of you who are contemplating Botox to do the microdermabrasions and light peels, etc before making this leap because it could compromise your health. Hope and pray that mine is only a short term reaction.

4/6/08
I had botox and developed a SEVERE headache the next day!
6/23/08
I have been getting Botox for years now (5, maybe?), and I always get a massive headache several hours after the injections. However, in my case, it is relatively short-lived (7-8 hours), and can be lessened with Tylenol or those nasty-but-effective Goody Powders.
Oddly enough, decreased frequency of headaches is one of the reasons I keep going back for Botox. I used to get tension headaches two, three, even four times per week; now, I get one or two per month, if at all. Botox lasts me a bit longer than it does some others, too - usually about 9-10 months. I don't need to wait for the remergence of my between-the-brow furrow to let me know it's time for more... the return of frequent headaches serves as my not-so-gentle reminder.
I can only speak for myself, of course, but I find that one nasty headache right after the injections is much easier to deal with than the many headaches I used to get (pre-Botox) on a regular basis. And, of course, the "added bonus" of diminished wrinkles makes Botox an easy choice (and a fabulous ROI!) for me.
I hope your headache was short-lived, and your results were not! -allie