My little peanut does this. It started when she was about 8 mos. old - she just turned 3. Our pediatrician tells us it is not uncommon, and she should grow out of it by the time she's 4 or 5. Also look up "breath holding spell" on the internet, you can find a lot of useful information, basically what our pediatrician told us. It happens far less frequently now that she's older, but still occasionally. I have noticed a correlation of frequency to when she is not feeling well, fighting a cold or something and/or extremely overtired. While it sure can be scary to watch, we were told the best thing is to stay calm and not make a big deal about it (i.e. avoid encouraging the involuntary behaviour?). I will also note that I had to switch daycare providers over this as they had never heard of such a thing and were concerned over their liability, etc. If you use daycare or a babysitter you should be sure to educate them in advance, even though our pediatrician made me feel like it is no big deal. Hope that is helpful!