I'm currently 27, male, decently in shape, though didn't always used to be (currently 205, dropped from 315 in a little over a yr thru diet & exercise)

Ever since I can remember, I've had this thing happen where if I stand up from a seated or laying position, I'll get dizzy and light headed, and if I'm holding my breath or stretching I'll black out. I went to the hospital for it once as a kid (~8-9) after I stood up and walked into the next room while stretching (think the morning stretch people do, arms up and wide, opening the chest) and passed out and fell against the wall and on the floor. They did blood work and gave me a checkup and just said to drink more water but nothing else.

It's almost like there's some restriction that prevents the full blood flow from getting to my head? Or something. To this day I can make myself start to black out, or even black out completely (which I admit as a kid I had a bad habit of intentionally doing because it felt cool) by standing up, stretching, and kind of tensing up.

Another interesting anecdote that may or may not be related, I used to donate plasma, and one of the nurses taking my heart rate & blood pressure prior to a donation said something along the lines of "hmm that's interesting, your heart rate fluctuates with your breath." And sure enough, if I breath in, my heart rate goes up and if I exhale or hold my breath it goes down. I can intentionally lower my heart rate to less than 60bpm just by breathing slower.

Also may or may not be related, I had SIDS as a child. Don't know the cause or really anything other than the story I was told that as a baby my grandma found me blue and not breathing and startled me awake and they hooked me up to some breathing machine after that. But that's all I know.

I'm writing because I know the answer is go see a doctor. But I feel I'm not good at talking to doctors, and feel rushed during the visit so I don't fully describe the issue and don't ask the right questions. Especially when it's not an acute injury I can point to and say "this hurts". Do you guys have any thoughts or ideas what it could be? Are these common symptoms people experience? Which kind of doctor should I even see, and how should I describe the issue? My insurance allows me to go directly to a specialist without a referral if I need. Or should I still first see a general practitioner? I haven't had insurance for many years, and never since being an adult, so I'm not great at all of this.

Thanks for any insight you may be able to provide.