Sounds like anxiety to me. There is no reason to explain why your pulse would decide to get so high while you're sleeping. You are probably waking up in an anxiety state. I've had the exact same problem myself.
I would wake up panicked, and with my heart racing. I then began to fear that happening so much, that I would wake up nearly every hour, jumping from my sleep. How did I make this completely go away?
I stopped fearing it. Once I lost the fear, I would still wake up in the middle of the night, but I began telling myself "It's ok that I'm waking up anxious. I'm just going to sit here and be ok, and maybe watch some tv for a few moments". In other words, once I began to stop concerning myself with waking up this way, it slowly began to happen less and less. This was happening to me just a couple months ago, and now it's not happening at all. It's simply because I decided not to care anymore if I woke up that way, and once I decided I didn't care about it, the fear was removed and it stopped happening.
In my opinion, this is the core element of defeating anxiety once and for all. Accepting the fears you're experiencing, and just not caring anymore when they occur. Because once your mind tells you to be scared, your body will react accordingly. If you control your mind to say you're not scared, so goes your body and the physical symptoms you're experiencing. It's not going to work instantly like magic, but in time it can happen.