I've been having the faint/sicky/hot feeling on and off through preg and have finally put it down to the baby lying on my vagus nerve at night (the one that can cause faintness and or palpitations. Just in case I drink lots of fluid too. And check with the midwife about blood pressure. But it could be the position of your baby lying on your nerve at night. I have to toss and turn all night going from one side to the next (palitations, hip pain added in too) and during the day if I get it I change position - sit on a bean bag or wobble on a ball. My seems to get relieved by big braxton hicks too, but no idea how to encourage one of those!