I get what you mean. I've had those moments. I would go several months at a time literally being a couch potato. Those are the periods of time where I would also suffer from headaches, dizziness, and nausea. Went to the doctor and they couldnt find anything wrong. I know its probably due to me being so sedentary.
I had to do research on obesity for a class and the things I found where very alarming. I just cant go on like this anymore. I'm scared I'm going to die young. Today is the 5th day of consecutive exercise for me, as well as eating healthy. I've been so paranoid that I always excercise even if I am feeling lazy. I dance for 20 minutes first thing in the morning, and hit the gym for another 30-40 minutes when dh comes home for his break (he works close by). Dh comes home at around 9 pm every night and if I am up to it, I spend another half hour at the gym. When I feel like giving up, I just tell myself staying active will prolong my life span.
I havent lost any weight, its that time of the month again, but I try to brush it off saying its not just about the weight anymore, its about overall health.