Lightheaded???

I am a 33yr old female, 5'3 and 220lbs.

I have recently started doing a Zumba class. This is the first aerobic class I have ever been in, and at the end we cool down and then stretch. I start to become lightheaded at the beginning of the cool down/stretch and then by time were bending over, I feel like I'm going to blackout and I see stars.

I've been working out for almost a year now doing cardio plus strength training 2-3 days a week. (My heart rate usually gets up to 165-174) So it's not like I jumped right into it, although I feel I get a better workout with the Zumba class. (not sure of my heart rate during this workout) My diet consist of fruits/ veggies and a protein daily. I drink plenty of water during my workouts. My blood pressure has always been fine and never any other health issues.

My questions are...Is this normal?? Will it get better?? Is there anything I can do to avoid this reaction?? I'm now only doing half the stretching because I'm afraid I'll pass out!