Touch ID doesn't work first thing in the morning?

Here's a weird one.

I have an iPhone 6 Plus, and the last phone I had was the iPhone 5 so this is the first device I've had with Touch ID. I'm using Apple's leather case and no screen protectors or anything.

I use it as an alarm clock and so sometimes when I wake up I notice there's something like an email I need to see immediately.

What I've noticed is that when I first wake up, Touch ID doesn't let me in. Like, it doesn't even recognize I'm touching it. I don't get the "try again" like I'm using the wrong part of the finger or wrong finger, the screen just turns off after a few seconds like I'm not doing anything. I have to unlock using my keycode. If I quickly lock my phone and try again it still doesn't work. If I try a few minutes later it works fine.

I don't think this is a hardware or software flaw, my guess is that there's something about my hands first thing in the morning that the Touch ID sensor has problems with but I can't imagine what.

Does anyone else have this happen or know why it happens? Or is it just me?