Also, I have had a few periods where I got worse (probably others, but these I know for sure):
Once during 2001-2003 when I was burning out (very extended, probably beyond 2003, but 2003 was the last burnout).
Once in January of 2008, when my grandmother was dying (and had died) and had lost a lot of my ability to socialize at all and refused to interact with people who did not live in the house.
And since November, when the noise level around here skyrocketed, my sensitivities increased, and some of them changed. I had many more shutdowns than I usually do (and I tend to have them semi-frequently), and I started showing more "autistic" symptoms, which is what prompted me to look into the possibility that I was autistic in the first place. It may be that my symptoms also intensified when I self-diagnosed and then when I was officially diagnosed, but I do not know since I was under a lot of stress which also makes everything worse at the same time, and I can't be arsed to try to separate the effects now.
I don't seem to be any less autistic than I was several months ago, though.