any chance the sweat got in your eyes? do you wear a headband to keep the water out of them? My treadmill has a pulse meter, what was your reading? Its a tough question to answer. sorry I can be much help.

The most obvious cause would be sweat in the eyes. That's accompanied by stinging (sweat is more acidic than tears, so it burns a little). Artifical tears (eyedrops) can wash that right out and as Skope wisely suggests, a headband will also help.

It could also be dryness. When you exercise, your body sweats, which can lead to dehydration. Keep plenty of water on-hand to replenish the water you're losing.

If you have a fan blowing on your face, that can also cause your eyes to dry out - you're blowing away the tears before they can replenish. Either direct the fan elsewhere or, if you're like me and need it there, just keep the fluids coming.

If it's a new occurrence then it could be something like a broken blood vessel. Doesn't seem like that's the case here though, if it goes away after you're done exercising.

Regardless, none of the causes are dangerous. Even if the broken blood vessel resolves on its own. So I doubt it's anything to worry about, although a call to your doc could confirm that. I'm certainly not qualified to make a diagnosis. :)

Thanks so much guys !