passing out during workouts

Have you been staying hydrated before the workout?

Make sure you are eating right and drinking water.....go see a doctor to make sure there is nothing else causing that as well! That does not sound healthy if you are having that feeling frequently.

Exercise-induced asthma maybe?

Always go to the doctor if you are concerned. That being said, make sure you aren't holding your breath during lifting and if you sweat a lot try and electrolyte replacement drink while working out. That can help. Good luck!

Hydration is key! I cannot stress this enough. Particularly in the summer months, when it's hot as hell outside and the gym air conditioning doesn't do as well. I can't really tell you what's up in your situation (doctor + pulmonary specialist are probably a good idea), but I have a fainting condition and get light-headed rather easily and I must drink at least 12 glasses of water a day in the summer. Fruits + veggies are a great way to get a bit more hydration in you (but don't count them towards your water total). I need electrolytes as well, particularly when running and I have to stay on top of my sodium...it's a tricky balance, but it can be done. Best of luck!

passing out as in falling down etc? or just feeling as if your gonna pass out? What does your trainer think?also if you have seen the Doctor regarding this what does he/she advise you to do?...there could be numerous reasons as to why this happens but I think its best you get your Doctors advice and follow it

What's your cal count like for the day? Even though you're eating right before working out - you might not be eating enough throughout the day. Especially if you are working out (and working out hard) you want to be eating more. When I was in the military I consumed around 3,500 calories a day and I'm only 5'3"! You have to feed your body. Get to a doctor and make sure you tell him/her EVERYTHING!

That happened to me when I was with a trainer, he told me I needed to eat (light) before my workout and stay hydrated during workout. Trainers usually push you more then you would do yourself.

You mentioned the doctor ran tests... did you have an ECG, or get the test done while under "stress", like on a treadmill? If boosting your hydration level (and lowering your caffeine and alcohol intake) doesn't prevent the light-headedness, I would tell your doctor that you need to find out what is causing this dizziness. You may have an irregular heartbeat ( an arrhythmia) that shows up when your heart is trying to pump harder to get blood to all your muscles. If it doesn't pump regularly, or has a slight jittery action, your brain won't get enough oxygen and you will feel faint. I'm not saying this is the cause, but it is possible. You need to know why this is happening. You don't want to find out when you are having a heart attack.

Definately see a doctor. Also, consider intensity of your work out. Is it too difficult (obviously this is felt) drop the intensity a bit. Don't sell yourself short, put out what you can, but pay attention to your body - listen. Even if that means dropping the intensity for a couple rep's. You can pick it up again when you gather yourself. After time you won't even notice that you wont need to slow down and you will be doing things you never thought possible!

When I see the tunnel closing into blackness, I "push" shoving blood back into my head. =P

Sounds like you are having episodes of syncope and/or near syncope. You need to return to your physician before you do anymore exercise. I would suspect that you will need a cardiac stress test, an echo (ultrasound of your heart), a 24 hour heart monitor, blood tests, pulmonary function tests and you should also be tested for orthostatic hypertension.
It is NOT normal to pass out, or almost pass out during a normal workout.

This is excellent advice! I know you said you've been to your doc for tests, but please make sure they've done all of what was suggested above. It's worth it for peace of mind alone!

I used to get super-lightheaded on occasion, especially during heavy workouts where I even completely passed out a few times at the gym. I went to my doc and was referred to cardiologist and neurologist for a battery of tests. They did full blood work, 24-hour holter monitor, echo, stress test, pulmonary function tests, brain scans, ENG/balance disorder tests, tilt table test...you name it. Turns out, I have orthostatic hypotension which, under certain conditions, causes a sudden drop in my already naturally low blood pressure--I'm normally at 95/65 and it would briefly drop to 80/50 or less and I'd just drop out. My cardiologist put me on meds to help my body retain more sodium, thereby raising my BP a little, but the meds caused their own set of issues, so they discontinued them and instead recommended I drink a sports drink rather than water when working out and stay well hydrated with water all other times; they have me wear compression socks, especially when working out; and they told me not to limit salt on foods--I don't go crazy on sodium, but I don't severely restrict it either. This has all helped me tremendously.

I was hesitant to go through all the tests at first because of the cost and the hassle, but I can honestly say I'm so glad I did. Ruling things out is just as important as finding a cause. Having all the information, knowing what is or isn't happening with your body, will ensure that you can safely put your all into your workout without worrying you're doing more harm than good.

Good luck!

Glad to hear that everything is normal so far!