A piece of ceiling drywall has started to separate in the garage. Upon closer inspection there are 2 problems. First it looks like nails were used to hang ceiling, some have popped out, others loosening. The other problem is the edge that has actually separated and is hanging down (a couple of inches gap) doesn't really even hit the joist - I don't know how or if any of the nails even hit the joist in the first place. The adjacent piece of drywall is almost flush with the edge where I should re-attach the sagging piece. I see others starting to sag in similar way

I plan to use screws next to all the existing nails/ nail holes on all sides and middle supports but there it will not be possible to put screws on that one edge unless I somehow angle them. The ceiling is just roughly finished so "looks" isn't a problem - I just want to get the ceiling re-fastened in the most secure way - any suggestions? (there is no moisture damage, etc. - it appears drywall is falling only because of how it was originally hung)