please take the time to read this and give me your opinions.
Sometimes when I stand up to walk my legs get a studded exhaustion to the point if I keep going they most likely will give out on me. A lot of the time It's followed with light headedness and my vision going black. It's will happen to me about 3/4 times in one day on a bad day others maybe 2 times. I know I would say on an average it happens at least 1-3 times in a weeks span.
Unfortunately it is unlikely people on this forum would be comfortable offering medical advice. Therefore I would suggest you please seek a medical consultation as soon as you are able.
Qualified medical advice is worth ten times the opinions of even the well meaning folk on this forum. See your GP as soon as possible.
You really need a Doctor to figure this one out. Please do seek qualified medical assistance. Hope it goes well.
You need a doctor.....
Go and see a doctor 
I am sorry you are worried. Sometimes being scared can stop us from doing what we need to do. Definitely book to see your Dr or the practice nurse might be able to help you.
I echo the sentiments of everyone above.
If you are a worrier, like me, something I learned during CBT to help me with anxiety may help you out - when you worry about something, try and identify it as "practical worry" (worry you can do something about - "What is that funny noise my car is making? Could it be something dangerous" action: take it to a garage) and "hypothetical/what if worry" (worry that you can't do anything about... "What if I crash my car tomorrow? What if my colleagues don't like me?").
For hypothetical worry, you can only distract yourself from it or allow yourself only a certain amount of time a day to think about it. Otherwise you get in a cycle of pointless worrying.
With practical worry (and I would certainly class what you're experiencing as something you can be practical about), you need to identify what you can take action on and how, and then take that action. And, as others have said, the action in this case is to see a doctor as soon as possible. But try to let the doctor do their job and don't let yourself get into a "What if X is wrong with me? What if I have Y medical issue?" worry, as that is hypothetical worrying! Try not to Google your symptoms either as you will no doubt find the worst possible diagnosis.
Wishing you all the best.
Hello all - 71 years old and hoping to run!
The struggle is real! 
