Heart rate increasing to over 150 bpm while standing up

[Alyssa_pryor]

I'm a 16 year old girl and over the last several months I've dealt with a lot of dizziness, fatigue, fainting, (or more normally just getting really close to fainting)  nausea and vomiting. I told my doctor about this and she thought it could be related to my migraines that I've had for years. My blood pressure has always been normal when the nurse checks it as well as my pulse. But I've become more aware recently how much my position effects my symptoms. If I'm laying down I'm perfectly fine, but as soon as I stand up i feel dizzy, lightheaded and overall just weak. I decided to check my heart rate change from laying to standing since I have noticed that my heart races when I stand up and was honestly shocked by how high it got. After lying down for 10 minutes I checked and it was at 88 bpm, which is pretty normal esspecially since I'm young and not particularly active. However when I stood up my heart rate instantly jumped and was at 144 after a minute. A couple minutes later I checked it and it was at 156. It went up and down a little but after 10 minutes it was still at 148 bpm. During this entire time I tried to stand still but had a lot of trouble and ended up having to lean against a wall to keep from falling over. I'm going back to the doctor in a couple of days and know that the internet cant diagnose me but want to have some idea what might be going on and possibly have something to suggest to my doctor to look into.