How come after two weeks of great vacation I am having trouble getting back early to work and focus on my assignments?

I am feeling a little bit strange, like I never been on vacation at all. Feeling so weak with no motivation to do anything. Am I the only one who felt like that after a long vacation?

I’m trying to get back to myself, but nothing helped so far.
If you did, how you got back to the real world of work and family?