I get moon-face at 40mg, and it seems to happen overnight after taking it for a week or two. As soon as I get the moon-face, my colitis symptoms seem to start improving.
Also, instead of insomnia, I get fatigued. I know that I am in the minority on this one, but I have no issues with falling asleep while on Pred, and while I wake up feeling completely refreshed, righit around noon, I crash hard. I used to go out to my car on my lunch hour and take a power-nap, which helped.
The worst symptom for me is headaches. Terrible headaches, which again is odd because cotizone is sometimes prescribed for people with headaches! But I had issues last summer while on 20mg-40mg of pred until I stepped down to about 15.