I have that problem if I'm working out and going at it way to intense. When your doing step or any other kind of physical activity you should be able to talk (or yell at the kids in my case) I have a bike that both the arms and legs move. I'm not kidding 8 mins. and I almost passed out, so the next time I focused on my breathing and when I started puffing I dropped the arms and slowed down. I was able to stay on for 15 mins.
I really hate admitting it but I'm really out of shape so slowing down helps me hang longer. I have a step video (don't laugh it's old) with Susan Powter, she continually tells you to modify and has many different people with many differnt fitness levels on the tape, I'm not the only one that fling my arms around for the full tape. When you are full speed into it and you stop like that dosen't that make it worse? I found if I'm really bluish green, puffing hard and need to stop I have to march in place or walk.
Oh and by the way welcome!!