Brand new day, brand new week. I hope you have a very happy day. If nothing is going on in your world currently that makes you smile, try re-running some old memories.
Instead of "Oh, it's Monday", and dreading the day and the return to the work week, why not throw yourself an unexpected curve and add something to your day that makes you feel like a kid again. How about ice cream for lunch? Or make a paper airplane? Or take off your shoes and go barefoot? Or eat lunch outside?
Do something that makes you smile and enjoy a "Happy Day".