Congrats on getting serious. My knees were so grateful to me when I did!
I did the hcg diet a few years ago, and found it amazing. I chose to do it under a doc's supervision because a) I have multiple physical issues and challenges, b) I needed the leverage on myself for the cost, and c) I know myself, and I needed someone to call when things are weird. And losing that much weight that fast, no matter how it's done, things get weird.
I used the homeopathic version, and I bought a 'kit' from a naturopath and he followed me beginning to end (with measurements of weight, blood, etc), and his office staff was unendingly supportive. The kit included ketone test strips, vitamin and mineral supplements, detailed directions, etc.
The thing I loved the most about that, was one of the snack supplements. It was a veggie drink and it was chocolate flavored. I KNOW that sounds horrible, and I was horrified when they told me about it. But I am a complete chocoholic and it made me not feel completely deprived of my chocolate fix. It was really surprisingly delicious.
I am getting ready to do another round, and I think I'll do it a little differently this time. And likely without supervision, since I'm more familiar with it.
For me, the de-tox was the worst. I think I had a monster headache/bodyache for about 3 days, from the sugar and caffeine withdrawal. The list of foods one can eat for the 500 calories is pretty small, and extremely clean. It's basically clean meat and veggies, and I had half an apple for breakfast. When I do it again, I think I'll go 600 or 700 calories and just have a slower weight loss. I lost about a pound a day for twenty days. I got very cranky and ended it at 22 days, they say that's the minimum. I read the paper by the doc who 'invented' the diet (after) and he did say that if you're especially uncomfortable you should stop.
I turned some friends on to it, and not only did they lose a bunch of weight, but he ended up starting a catering business. Doing the diet brought out in him endless creativity at making the limited choices taste good and have variety; he then realized he loved that a lot, and is now a happy and successful caterer.