Nest Thermostat Question....

Every day I'm awakened at around 5am. I always thought it was a prostate thing and I had to pee.

This a.m. I think I found out why I'm awakened at 5am. My Nest thermostat's fan setting is set to run everyday between 5am to 9am. When the fan is triggered on - the noise wakes me up. It is not the biological trigger I was assuming it was.

I don't remember setting it that way and am wondering why one would make such a setting?

Why is there a fan setting on the Nest and what is the best way to set the fan on the Nest?

Is it important that the furnace fan be set for proper functioning of my furnace? Is it an energy saving function?

I'd for once like to get a good nights sleep and not be awakened at 5am every day.

What should I do?