Unexplained Night Chills and Sweats

I've been experiencing this strange sequence of events over the past year or two, and I can't find anything that explains what might be causing it.

Every single time, this is what happens:  I wake up during the night with an intense, bone-deep COLD feeling.  My teeth are chattering and I cannot seem to get warm.  I'll be so cold that I can't even bring myself to get up and get another blanket.  I'll curl up in a ball under the covers, shivering, and praying to get warm.  I've never in my life experienced such a thing.  It's awful. (I live in the northern U.S. which of course has frigid winters, and I've had normal chills before, where you get cold and can't warm up.  What I'm talking about here is something much more intense than that.  I don't think the word "chills" suffices, actually.)

I will fall back asleep, and when I next awake, I am in puddles of sweat, completely drenched.  Now a person might think this is because I was all curled up, but remember these are the same covers I'd been using all night, so there is something going on with my body that is causing these chills and sweats to happen.

I'm a 40-year old woman.  I take some medications for cholesterol and migraine prevention (Gemfibrozil, Simvastatin, and Atenolol).  Some of the medications list chills as a possible side effect, but this recurring theme of night-time intense cold followed by sweats is more specifically what I'd like to find the cause of.  It may only happen once every couple of months for me, yet I'd sure like to figure out what is causing it.  

Normally, I prefer a cooler room to a warmer one. I am not someone who tends to be cold a lot.  I don't have Reynaud's Syndrome, I do have hypothyroidism but my thyroid is regulated with levothyroxine and my levels have been consistently normal for years now.

Any insight would be greatly appreciated!

[Caryopteris]

I think it's hormones.  Dr. Oz has good information if you want to check out his website.  

[taaju]

t same 4 me but durind early morning