A few years a go I weighed over 315 pounds. I decided that when going up a flight of stairs winded me, it was time to do something. I felt like shit, looked like the Comic Book Guy, and slept horribly, always waking up in a sweat and never getting a good night's sleep.
I went to a personal trainer, started working out 2, then later, 3 times a week and quit drinking Dr Pepper and eating Pop Tarts for breakfast lunch and dinner. I got down to 236 pounds, my goal was 225, then a project crunch at work hit, they bought us dinner, free sodas all day long and I got lazy, again.
Went back to 271 pounds when I started the Atkins diet. Now I'm down to 244, still shooting for 225. This time I will not go back to Dr Pepper and Pop Tarts for food sources! The tips Tony stated above are dead on. When I was losing the initial 90 pounds, I didn't stick to a diet, I worked out (lots of cardio) and ate healthy, (non-fat, no processed sugar.) I just made the classic mistake of not keeping it as my regular diet, I went back to the dark side... Mmm dark chocolate....
After losing all that weight, it's wasn't an amazing rush of energy, it's more of a realization like, "Hey I can see my feet again!" or "Damn! I just ran a mile for the first time since high school!" After losing ~25 pounds on Atkins, it's noticeable again, more energy and better sleep. I highly recommend losing any extra weight you may be carrying...