Probably still just adjusting... you practically came home from another planet, when you think about it. Stresses out the system. How are you sleeping these days?
I've wondered if it has something to do with re-adjusting to the colder climate. I try my best to keep a regular sleep cycle, and I almost always go to bed around 11:00 pm, give or take 20 minutes at the most. I get up at 630 am at the latest. As for sleeping, my quality of sleep isn't great. sometimes I have a hard time falling asleep, I dream a lot, I wake up a lot, and sometimes i'll simply wake up after a few hours of sleep without being able to go back to sleep.
Do you think it could be linked to my metabolism?
My sleep pattern is identical to Andrews....
...but the main reason for mine is the fact that because I am at home every day and do little or no exercise, I frequently "cat-nap" throughout the day with the result that I need very little sleep during the night, constantly dreaming and waking up.
I have no problem with this because I know that during the past 24 hours, I have had sufficient sleep, overall...

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For anyone worried about weight problems, etc, I would advise visiting the Doctor* and obtain a Blood Test....It can often be put down to an over-active, or under-active Thyroid Gland (located in the front of the neck).
This regulates the metabolism of the body, and needs to be in equilibrium....

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If there are problems, it can be corrected with daily medication.
I take a small tablet daily to correct an under-active Thyroid Gland....keeps me in good order...

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Paul.... 8-)...!
* ..get your Prostrate Gland checked as well, while you are there...trust me...(It could save your life!)....

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Win 8.1 64-bit. DX11. Advent Tower. Intel i7-3770 3.9 GHz 8-core. 8 GB System RAM. AMD Radeon HD 7700 1GB RAM. DVD ROM. 2 Terra Byte SATA Hard Drive. Philips 17" LCD Monitor. Saitek Cyborg X Fly-5 Joystick. ...and a Briggs and Stratton Petrol Lawn Mower.