Woke up to fans running full, El Capitan on my MacBook Pro.

[PinkyMacGodess]

I woke up this morning, and walked by the couch where my MBP was sitting, plugged in, and sleeping.

And sounding like a turbo prop plane revving up for take off!

It was really loud, the fan(s) sounded like they were running at full RPM, and the case was HOT!!!

It woke up fine, but now the screen is darker than before. Like the ambient light sensor isn't working right...

So, was it having a 'nightmare'? Yosemite never did that.

This is an early 2011 with 8G RAM...

 

[PinkyMacGodess]

Weird...

I let it sleep again, and after waking up, the screen was back to 'normal'...

Odd...

 

[Fishrrman]

My simplistic advice to avoid stuff like this in the future:

At night, just shut the MacBook down -- power it ALL the way off.

Easy as that...

 

[randomgeeza]

I've seen this happen on my old MBP and my partner's MBP. It has also happened to me, on the my newer rMBP, whilst in a flight bag. I've always put it down to something glitching out. What... remains a mystery.