why do we hate goin offices on mondays???

That's because Monday is the first day after the weekend. From Monday to Friday, you spend the entire week trying to get into the habit of sleeping and waking up early. But during the weekend, you break the habit you were trying to form all week, by staying up late and sleeping in. Since you're already use to sleeping in, by Monday, you dread having to wake up early, making it all the more difficult to wake up. Actually, I was told that if you're always having difficulty getting up and going to work, it's a good indication that you don't like your job. This was just his opinion, of course, it's not some scientific fact kind of thing.