So I left my Note 4 charging overnight.

That's right. Charging it over night will not hurt the battery. Also, charging it every time using the fast charger will not hurt the battery.

I use the fast charger for both of my phones every time I charge.
 
Have you guys done this with your Note 4?

Posted via the Android Central App

I do it every night! Never any problem. I do it with my laptop, iPad, camera, video camera and anything I charge. Sure hope it's not a problem or I'll be replacing batteries for everything!