People say it's "just one hour" but it's one hour every day. When you get up in the morning you're now getting up one hour earlier. When you go to bed at night you are now going to bed one hour earlier. Everything is earlier. For me I find it does not matter at what time I go to bed, it's what time I get up. Getting up at 5am I will be more tired throughout the day than if I got up at 6am, for example. Does not really matter what time I went to bed at. But that's the other thing when I go to bed early, I'm not tired enough so I may not fall asleep as fast either.
There's also lot of physiological effects that it causes, which as you get older get worse. It never affected me that badly before but in the past few years I find it often starts to trigger depression. I figured out ways to prevent it such as trying to get more daylight, and trying to avoid sleeping in too much on my days off, but either way I tend to start to feel down for the few months following the time change. It's not just the time change, it's the season itself but the time change is the straw that breaks the cammel's back.