Fan turned off for a few days, then suddenly turned back on. How should I react?

Laptops have a built in heat sink. When it was not running it may have been because the unit was cool or the surrounding air was sufficiently cool enough that it did not require the additional fan running. The internal motherboard has a thermostat which keeps the fan off to save energy until the internal heat reaches a certain point. You should be ok. I usually add a pencil under my laptop just to ensure it gets more cooling air.