I realized about a week ago that I'd been shorting myself on sleep, and drinking too much soda. I've cut way down on the soda and cut back on my late night activities and after just a week I feel much better.

It really does make a difference.

I disagree.

I cut back from 4-6 sodas a day to zero for a little caffeine-free experiment I ran on myself. I was drinking no sodas for about 2 weeks.

I felt no different (after I quit having caffeine headaches, that is).

Thus, in my opinion, your difference is (very much nearly) all in the fact that you're now getting enough sleep.

I cut back on soda for two reasons - 1) my weight varies pretty linearly with my sugar intake, and I've been getting a bit pudgy of late. And 2) the caffeine prevents me from sleeping well. I can't say for sure if the drop in soda intake is responsible for my feeling of well-being but it certainly is easier on my wallet.