Nearly killed myself at the gym!

Today I ill-advisedly took a class at the gym called 'the Alesha Dixon dance workout' along with my sister and my mum... I had to leave early because I was gasping for breath after about 20mins nonstop! My sister and mum managed to stick it out for the full 45 minutes so I feel terribly ashamed, especially considering I go to the gym a lot more than either of them. I never do any cardio though which could be the problem.

Worrying when your own mum's cardiovascular fitness is better than your own!