How was your water intake that day? Only reason I ask is because a small handful of times when I didn't drink hardly any water throughout the day, I will wake up in the middle of the night (closer to morning) and feel so dizzy and like i'm about to faint, and likely much like how you felt. Although I never monitored my blood pressure when this was happening, I am sure it was very low, based on how I was feeling. Drinking some water would alleviate the symptoms after about 15-30 minutes of suffering. I'm 100% sure that what I have felt those couple times, was from lack of water intake that day. Some are more prone to the affects of dehydration than others, and some respond different/worse than others.

Dehydration can cause blood pressure to drop, it's something you should also be conscious of in addition to the results of your tests at the cardiologist; which I definitely second the recommendation to go get checked.