2 to 4" is extremely thick, beyond normal.
If it is that thick, the weight would be suspect.
More info to be certain, is there wood lathe?
did it also come down? Did nails come down?
You should use 5/8" drywall, not 1/2" on a ceiling.
I would advise against covering the exsisting ceilings.
A proper repair would be to remove the old ceiling
and replace it.
If you remove the ceiling, it would be a good idea
to inspect and replace any aged plumbing or electrical.