Hey
my cousin has the same problem. You might be suffering from night terrors. During one of the stages of the sleep, a person might scream, run or break something etc. It is usually during this time that the heart rate increases. The interesting part is that most of the people don't even realise what they are doing (even though they seem to be wide awake and in their full senses)
as long as the behaviour is not destructive or harmful, I don't think there is anything to be worried about.
If you are really concerned about it, I will suggest you ask some one to sleep in the same room with you for few days. Or you may go and see a psychiatrist.
I hope this will be of some help to you.