Nearly didn't go (kept coming up with excuses) but in the end bit the bullet and went to my class.
It's called Body Attack and it's the toughest cardio class I have EVER done - the class is full of fit girls and I hang out at the back puffing hard with my red face! But it's so worth it, you feel so high afterwards, knowing you've burned all those calories!
I couldn't keep up the high intensity all the way, but I didn't have any extra breaks - just kept jogging on the spot or something when I just couldn't do any more squat jumps!
BUT I know it will get easier, as I remember to go every week!