I almost collapsed after doing cardio workouts. how can i prevent this from happening again?

Get checked.: If you truly nearly collapsed after a cardio workout, this must be considered a warning symptom for possible heart disease. Others include chest pain; shortness of breath; pain or pressure in the jaw, neck, arms; light-headedness, dizziness or unusual fatigue. Now, if you're really overstating the concern, scale back and take it slower until you build up your fitness. Err on the safe side, though!