Why do i get a fast heart rate, shake, and get a little headache at random times. it does mostly happen at night but it also happens during the day.

Many possinilities: Hard to tell from here. I'd see if there is any temporal relationship to certain eating habits or food items, and relationship to specific activities? Do you ingest a lot of caffeine? Any consumption of energy drinks? Any recreational drug use? If not, I'd see a doctor and get a 30 day event recorder, a device you can activate when you have these racing spells to see if rhythm abnormal