Maybe it's a type of "cabin fever". I grew up in the north, and there were always stories about a baby boom 9 months after a big blizzard.
What else to do when you are shut in? Beats jigsaw puzzles I guess.  
IMHO you are being a normal healthy human.

OK! Now we know you're not a bear! :)

Yep! Me too! The heat of summer tends to tap my energy unless I'm hanging around water (pool, ocean, etc.), or I'm in a well air-conditioned place.

Well, scoed,

It appears that you are within the normal distribution range of "horniness," although in Scandinavian countries, there is a statistical "baby bump" in late April - early May, meaning that people engage sexually more frequently when there is more daylight. Scandinavia in particular has very brief periods of darkness in the 24-hour cycle during June-July - hence those long summer nights of frolicking. You may be less affected by your own circadian rhythm than some others who tend to lose energy and sex drive in wintertime when days are shorter.

Hope that makes sense,
The Love Goddess