Wow B.,
You have a ton of responses here! My daughter also did this, and I had no idea it was so common. Of course, the first thing to do is get her checked out by the doctor. Barring any medical reason, you can try some other techniques.
Many here are claiming it as a temper tantrum, but here is how our doctor explained it to us. It is NOT a temper tantrum, at least it doesn't start that way. He told us that when our daughter got very scared, angry or hurt, her brain and body were literally bombarded by stress hormones. Because she was so small and inexperienced, her brain didn't know how to handle it and would have these "fits" to basically reboot the system, just like when your computer freezes up! This totally made sense to me. The fits started when she was super young, and they happened whenever she was very hurt or angry. As she got older, they got more and more rare and mostly happened when she was hurt. I think she had her last one when she was about 2-1/2 and she fell and hit her head really hard. She is 3-1/2 now.
He did say that if you give a child excessive attention for it, it can become a learned behavior. How much attention is excessive? Well, that is up to you as you know your child best. I always held my daughter and rocked her for a little bit, then encouraged her to get up and get on with life. (When she was nursing, this was a surefire way to calm her down immediately, as well as provide her with loving care.) I understand the reasoning behind parents who say just ignore it or put them in their room. I personally felt wrong ignoring my child who was hurt just because this "fit" is how her pain/fear manifested itself. If she fell and scraped her elbow and was crying, I wouldn't put her in her room until she was done with her "tantrum." You have to decide how much attention is the right amount for your daughter.
One thing that can help, is to work on giving your daughter positive ways to express her emotions. We started when my daughter was about a year old helping her to name her emotions. We would say something like "You are really MAD at Mommy! You wanted that book and Mommy took it away! You are MAD, MAD, MAD because you can't have the book." That was it - no judgement, no shouting about how she can't be mad, no punishment for showing her emotion. When she calmed down, we would explain that she can't play with Mommy's books, but we could get one of her books to play with. I wanted to acknowlege how she felt, to teach her that there is nothing "bad" about how she felt, but that she needed to express it in a different way. I think this helped her learn to deal with her emotions in another way other than having fits. A great book to read about speaking your kid's language is "The Happiest Toddler on the Block" by Harvey Karp. It helped us a lot.
Best,
S. L.