As posted above, there are dozens and dozens of things that could be causing this and it's hard to say because I don't know what kind of shape you are in if you are overweight, etc.-- I'm guessing not if you you were a gymnast-- but up until what age. You lack of cardiovascular performance could be just an underdeveloped cardiovascular system due to a sedentary lifestyle or a pulmonary/breathing issue. One of the things though that does raise a flag and points to a heart or heart valve issue is when you say you got black-outs when quickly getting out of bed. Your heart fills differently in different positions and if there is something wrong with your valve (most likely with your case, your mitral valve) which is involved with heart filling this could be causing the black-outs. do you get annual check-ups and if so have you have translated any of this on previous visits.
Either way, go see a primary doc ASAP and describe everything you have above and write it in the survey they give you on your first visit. Have you had an echocardiogram done yet? If not you should. Make sure you go to a respected echo lab-- it's important to get a good echo. Make sure they do a comprehensive job evaluating your mitral valve. They should do doppler on the valve and color-flow (colors through the valve to look for any leaks). You might have something called mitral valve prolapse which is common in females. You might also have some congenital heart condition (too many possiblities to list here). You should probably also have an EKG. If you don't know what an echo is, just do a search on the internet for "echocardiogram"
As far as the anxiousness and nervousness, that could be a completely separate issue or it could be related. it's possible if you do have a heart condition it could be making you anxious.
When you go to the doc he or she will probably start by listening to your heart and breathing with the stethescope. Make sure you tell him/her about that thing with the black-outs when you get out of bed quickly-- that's significant and very useful information. Of course most of us are a little light-headed when we get out of bed because the blood is rushing from our head to our legs, but it should not cause a black-out. That is why to me, that is the most eye-opening piece of information that you have provided. The other stuff could have hundreds of different explanations. But, the black-outs if they are not neurologically related, lead me to deduce that it is being caused by your cardiovascular system, more specifically your heart. I suspect some of your anxiety is due to your past criticisms. That might just be a side issue, or not. Just get to a doc, provide all the info above and have them give you a prescription for an echocardiogram and EKG. If you are under 18 you need a pediatric echocardiogram, which has to be interpreted by a pediactric cardiologist.
You won't get answers until you get these diagnostic tests done and see the doc. The information here is not specific enough to give any answers yet, sorry. Good luck!
Sorry, forgot to say. I use to have black-outs when getting quiqly out of the bed. And faintings when I was little. I didn't do any kind of tests when that happenned, I was little, my mum was ignorant, sorry to say that. Right now, I did so far blood analisys-ok and EEG-also ok, and RMI-also ok. Please give me some answers.
Could be anything, could be heart..could be hormonal, could be just diet..go to a doc and tell him what you typed here.