It sounds to me like anxiety. I'm not a doctor but I do experience something similar. The doctors think I have PSVT and after my last episode I've been so worked up about having another that it has induced a sort of panic in me at night. I will trail off to sleep and wake suddently (either to go to the bathroom or because my dog bumps me), and the second I open my eyes I become completely disoriented and my heart goes nuts. Once I talk myself down and wash some water over my face I feel a bit better. This is how I look at it... if there was something really wrong with my heart, wouldn't it show up at random times throughout the day and not just between midnight and four am? I hope this can help you rest a bit easier until your next medical appt. Take care!
Anxiety, depression, and panic call all cause crazy body functional mishaps, including irregular, high rate and hard/heavy heart beats. This doesn't mean that a heart rhythm problem is driven by one or all three of these emotional states, so it is best to discuss with a doctor who will make some tests on the heart, at lest an electrocardiogram and a good long listen with the stethoscope. Many (most?) primary care doctors should be able to determine if you need further diagnostic work by a cardiologist.