Why do I get a cold after I exert myself past my limits?

Today I had my interview and physical testing for the national search and rescue team. I passed! Yay!

Anyhow, part of the physical testing was the beep test. I was moved in to an earlier time slot so I was not as prepared as I wanted to be. I also seem to have a tougher time doing cardiovascular exercise in the morning versus the afternoon / evening. I was allotted time to warm up, but I (stupidly) didn’t take full advantage of it and wasn’t fully warm before I started the test. About 3/4 through, my lungs were burning like mad. I kept going and pushed very hard, and by the end it felt like my lungs were on fire - it almost feels like they’re bleeding, but I’m sure they’re not. I finished up, then did all the other tests (sledge hammer, pull and drag the dummy, lifting and carrying heavy stuff and ladders, etc.).

Before the tests, I was fine, felt almost 100%. Immediately afterwards, I started feeling like I was getting a cold. I had a painful cough and within about 10 minutes I started sneezing. It progressed to a full blown cold within an hour, and here I sit with a stuffed nose and wads of tissue.

This isn’t the first time this has happened. I’ve pushed to the point of burning lungs before and about 75% of the time, I end up with a cold afterwards. Is this coincidence or something else?

Also, what is happening in my lungs to cause the burn (which is gone now - I even went for a run this evening and my lungs were fine. Good thing I brought tissue though!)?

Overexertion can depress your immune system. You may have already been coming down with it and it was not apparent until you pushed your self.

That quickly though?