Please help.
I have a vivarium, it is half water half land and an apple snail. The snail was about to lay a clutch of eggs when it was startled and released from the wall. It hit a wall and I knew I heard a crack. Upon inspection there was no injury. Since the snail has not moved, she is half exposed to the water and I am very afaid that this injury is going to be fatal. Please advise me, I have removed her from the water to protect that spot from more water entering, I have seen her lay eggs for 3 hours so I know she can survive out of water for a while. Please any advice?

well in the minute that it took me to type my question my snail has moved back into the water and has half (*the side with the injuy) of her shell out of the water. I will leave her alone, but would still like any advice out there. Thank you.

today the snail is just attached to the side of the tank under water, I have feed her but she did not eat, which is very odd for her. Also it seems I forgot to mention that there is a whole in her shell. It is about 1/4 inch wide and maybe 1/2 inch long. the gash is black, I assume she has formed something like a scab over the spot.

While she can live out of water for a while, she would eventually dry out so it's best to leave her in the water which it sounds like she's there now anyway. You could maybe seal over the hole with something like they do with injured turtles but it's probably not feasible to do that for most people. You can apply antibiotic to the hole like the new Biobandage they sell to smear on fish wounds; I think it's safe for snails and might help prevent infection. Infection is the main worry. Be sure to keep the water very clean and add some aquarium salt (a tablespoon per 3 gallons or so) to help prevent infection. If it seems to become infected, add some fish antibiotics to the water like Maracyn by Mardel. She may have some internal injuries which you can't see but the inside of a snail is pretty fluidy so it's not as likely as with vertebrates to have injuries inside from a fall. She is probably still a little stunned from it. Hopefully, she can recover.