I went biking yesterday and covered just under 12km. I was going at a relatively casual speed, though would go quicker when going uphill. I do this trail often. About 8km in I felt all right, I was a little sweaty and tired but still felt energized. Once I reached the top of a big hill, the second I stopped, I felt absolutely exhausted- I could barely stand or do anything. I couldn't get enough air, was breathing rapidly and I thought I was going to faint. It was quite scary, and I struggled for balance and was incredibly nauseous. It lasted a long time, and while trying to recover I kept having to stop because I could barely walk. I am still on a waiting list to see if I have exercise-induced asthma, so I believe my difficulty breathing along with the heat and humidity may have caused heat exhaustion. I'm positive that if I'd kept biking the way I had been for another five minutes I would have passed out, vomited and been unable to breathe, and that I may have been in a dangerous situation. With what I've described, is it possible that I had heat exhaustion? What can I do to protect myself if I find myself in similar circumstances again?

Could be heat related. Could be lack of fluids related. If an altitude was involved, could be altitude related. Or you might have had a bug.

Drink mucho water next time. Wear light covered clothing. Don't drink alcohol in excess the night before. Since you had this episode start with some shorter distances and see how you feel.

In high heat and humidity, simple, don't over extend yourself. Could be heat stroke that effected you.

How old are you ?

As long as you have to wait for the test, why not get a more general checkup at your regular doctor's?
Very few symptoms of any condition can't be attributed to a number of causes.
So sure, it sounds like heat exhaustion. You've seen the marathons with people collapsing, getting wrapped loosely in a mylar blanket, and hydrated in the shade. I'm sure you carry a water bottle and take sips as you go, right?

Have your blood pressure checked and heart listened to, and check your family history for strokes and heart attacks and when people died, and of what.
That and more are why we go to doctors in person! We don't even know your age, weight, and general health.

Just listened to an eye doctor list all the information that can be detected by looking in the eyes. GPs don't seem to do that much anymore.

I would certainly take a break until you do get properly checked out.

As long as you have to wait for the test, why not get a more general checkup at your regular doctor's?
Very few symptoms of any condition can't be attributed to a number of causes.
So sure, it sounds like heat exhaustion. You've seen the marathons with people collapsing, getting wrapped loosely in a mylar blanket, and hydrated in the shade. I'm sure you carry a water bottle and take sips as you go, right?

Have your blood pressure checked and heart listened to, and check your family history for strokes and heart attacks and when people died, and of what.
That and more are why we go to doctors in person! We don't even know your age, weight, and general health.

Just listened to an eye doctor list all the information that can be detected by looking in the eyes. GPs don't seem to do that much anymore.

Oh and why not alarm unnecasily, gosh. Eye doctor ! Joy, can you just take a break !

yes, blood pressure and complete work up. and again, how old are u