Anon, thank you for your personal account. That's not waffling at all!
Personally I found it was difficult to quantify because "energy" was such an odd concept to me. I went through a phase of trying to booze my way through anorexia and depression, I tried spite-eating, which was just eating whatever I was told to despite my own hatred of it (if you've been admitted, you'll know this), and then, binge-eating. None of these yielded a real response other than weight yo-yo; but if you think about it, it makes sense that way. Why would your body react positively by being scammed, plotted against and thrown against a wall for a response?!
It wasn't until I accepted I was wrecking myself and that I would need to be normal for a while that I started to appreciate normailty for what it was. WOW. What bliss. You know something - the best thing I ever did was let someone else dictate my diet for me. It has to be someone you REALLY trust, but if you can, this is a HUGE boon to you.
You let a "normal" person dictate a "normal" life. Sounds simple, because it is. Initially I let mum do it for me. Make my dinners for me again as if I was a child. But then again, an ED turns you back into some fussy little brat kid in many ways, so it's appropriate. It's why I view ED sufferers as "adult children" because that's all they'll ever be.
With the control out of your hands, you begin to accept you can't go, "Oh, potatoes. One. Two. No, ONE potato. One. Oh, I could cut the potato in half. Half a potato. That means I could weigh the potato. Oh, then I could cut the potato into small cubes and...." and it begins again. With someone else telling you, "Whoa, man, what's the deal? THIS is your dinner, EAT IT" - you slowly accept that things are not always within your ninja-like grasp.
Eventually, after accepting the meals and judgement of a friend for a long time, I started to get a night's sleep. I started loving the feeling of my pillow again. I started filling out my trousers. I started to get sexual feelings again. I started to have dreams. These are all things you have no idea how much you missed until they properly return. When you body is starved for so long, if you merely eat to "maintenance", you're not really healing. That's like saying "There are one hundred cells and in the past, you'd feed twenty cells, so eighty died every day. Now you're eating for one hundred cells, so the dead cells are forever dead." You need to accept that energy is necessary to rebuild your ravaged, rotten body. And it is just that - rotten. The tissues have rotted away to nothing so you could be slighter. Nothing glamorous about that. Same deal as having beasties eating away the tissues in your body. People don't look at you and think, "wow, they're slim!"- they think, "Oh, that poor person, what tragedy befell them?!"
And imagine you're on the lookout for a partner. Not many potential partners look for "Physical and mental tragedy" on the top of their lists - and if they do, they're likely to be sufferers themselves.
So long story short - energy levels only returned to me after about 20 months of recovery, and I am now almost BMI 22. That's a long, LONG time. The longer you've starved, the longer it'll take to be a full human again.