Don't worry, you don't do all the levels in one day! You start by doing level 1 every day, then when you feel ready you move to level 2, then level 3 when you're ready for that. I'm planning to do 10 days of each. Just finished day 2 of level 1 and I won't lie, it's very difficult, but despite my complete lack of fitness I finished it without stopping on both days and the sense of achievement is brilliant! It's split into circuits, so just when you feel like one particular exercise is about to kill you, it changes, which I find really helps to keep me going. After I've completed it I feel so happy and energised! It's definitely worth doing!