I am very new hear, but just met with my exercise counselor on Friday. With you not getting any exercise now, all you probably need to do is move. I am like you and it took about five peddles of the bike to get my pulse rate up to aerobic level. I warmed up on the bike for five minutes, then did about 20 minutes of resistence exercises, all the while my hear rate stayed up. I am supposed to exercise 3times per week for about 20-30minutes at a time. I know as I get healthier I will have to increase my intensity, but right now, I feel that this is SO doable. The first step is to get up.