It seems like fatigue.
I would avoid working out tomorrow, but maybe stretching it a little after a long walk (you don't want to stretch cold muscles). If the pain persists or gets worse I would see a doctor.
I have a certain feeling that it isn't a matter of night or day. Three probablilities:
1) Your light is broken and you don't notice it during the day,
2) Your clock is set incorrectly and it thinks it is nighttime when it is actually day time, and visa versa,
3) You have the adjustment all the...