muscular pain.......!!!!!

I'm in pain now. Incredible muscular pain everywhere! (snif snif...)
On Sunday I finally tried to end my lazy life and went to the gym downsatair of my flat (Mel&Marta, you guys encouraged me!). There was a trainer who I could talk with quite friendly. I took his training class of 30 minutes called "Shape&Pump". This is a combined exercise of aerobic and muscle exercise, never stop moving during that 30 minutes. I have to admit that it's been months I haven't been to the gym and I used my weak muscles suddenly so intensively, they just broke down their system...These couple of days, I move so slowly and I feel that I can understand how it's like to be an old lady. I really feel depressed when I see long stairs ahead of me and I climb up/down with holding the bar so hard.
This is the cost I have to pay after lazy days over months. I'll try to go to gym at least twice a week, ideally 3 times a week!!