I only use to ride the treadmill ocassionally, but already twice this week, my younger brother asked me to accompany him to the gym. So for two days we've been using the automatic treadmill as a warm up phase. Only question is, why do I feel dizzy (only mildly though) after a cardio session on the treadmill, while my brother doesn't feel dizzy at all? :confused:

approaching illness... (cold, flu, etc..)
not enough food
not enough water
not enough sleep
holding breath

Any of reanimated's guesses or even not cooling down. At the end of your run, you should gradually scale back your running until you are at a brisk walk and finally a moderately paced walk. This scale back (cooling down period) should take at least as long as your warm-up.

Well I think cooling down is not the case, since I'm doing the program according to the treadmill, where you do it for 20 minutes. You start with walking, jogging, running, jogging and walking again.
Holding breath is also not the case, since I always do some conversation with my brother... Anything else, aside from food, drink and sleep?

IMO, it may be water cause it's really hot in that gym? Possible?

Just to be cautious - consult with your physician.

You know- I bet it has something to do with the motion of the treadmill. I have the same issue; I can do an hour of any other type cardio, any intensity. But an easy 20 minute stroll on the mill makes me momentarily lightheaded. Could be a simple equilibrium issue.

This happens to me occasionally...less dizzy and more light headed.

Were you watching a TV while you were doing it? I can tell you that certain images on the TV give me motion sickness during cardio. If there is a lot of flashing images or motion simulation (like riding in a car) I am affected.