Sounds like night terrors to me. They're a little different from nightmares in a couple ways. From what I've read
1. Kids can't usually be awoken from night terrors like they can nighmares
2. If you try to intercede or comfort your child you could just make it worse, as opposed to a nightmare where waking them up and comforting them might be more helpful.
3. Night terrors usually are more dramatic than nightmares, and their eyes can be open without the child being awake (kind of creepy, but it happens a lot)
4. They happen often times because of lack of sleep. If the child is missing out on sleep or naps due to teething or illness or life in general, their body goes into a deeper sleep mode when do fall asleep, and this somehow brings on more vivid dreams, as though their mind is packing a lot of dreams in all at the same time to get them processed through the grey matter.
Night terrors do subside after a few weeks to a few months. They are not harmful to the child, but are actually beneficial for their mind and body (though I can't see how!!!).
If you want to protect your child as well as prevent these from happening so much, some ideas would be to
1. watch over him while it happens (if you can do so without breaking down and interfering with the dreaming), and make sure he doesn't get into any trouble or hurt himself. If you can't watch him yourself, either have your husband or another family member help, or make sure and "injury-proof" the room before he goes to sleep by putting padding on sharp corners and by locking the door so he doesn't go out and wander around the house or yard (I know he's young, but maybe he's really agile???)
2. notice what time the terrors are happening each night and try and wake up your son before that point. He'll fall back asleep in no time and most likely have more calm dreams
3. be sure he's getting as much sleep as his growing body needs, when possible.
An 11 month old boy should be getting AT LEAST 10 hours of sleep a night and then another 2 to 3 during the day. Ideally he needs to be going to bed around 7:30, 8:30 at the latest, each night. Any time past that and it's harder for him to get the full, deep sleep he needs, no matter how late he is sleeping in. If he's sleeping for 11-12 hours at night and getting another 2 to 4 during the day, you're definitely doing well. It amounts to 13 to 15 hours a day.
Babies are more inclined to sleep problems when they are sleep deprived, but it's so hard for us to know sometimes when their little lives change under our very noses, so don't beat yourself up if you find that getting him to sleep enough is a struggle. You wouldn't be the first!!!
If you think he is sleeping regularly and deeply enough, then just keep up that schedule (until he's ready for a change in another 6 months, of course).
Here are some links to information about night terrors and sleeping if you'd like to read up on it.
Toddler sleep habits:
http://www.babycenter.com/0_establishing-healthy-sleep-ha...
What are night terrors:
http://www.drgreene.org/body.cfm?id=21&action=detail&...
What are night terrors:
http://www.babycenter.com/0_night-terrors_142.bc
Good luck and don't worry. They'll subside soon!
Mom of a toddler