tiredness in summer?

[FilthyMack]

Why do so many folk feel especially tired in the summer if you have a sleepless night and it isn't necessarily hot? Is it something to do with chemicals been released in your body by the sunlight?

[FTVS]

I thought most people felt better in summer due to the chemicals relaesed in your body by sunlight...? Howveer personally I often have trouble sleeping in summer but I think this is because it gets light so early and wakes me up.