Nerite Snail Troubleshooting

i have a nerite zebra I got from my LFS about a week ago in my 5 gal betta. pH is 7.0, temp is around 77-78 throughout the day. The snail has barely moved since I've gotten it. I know it's alive because in the morning, it's in a slightly different place and when picked up, the trapdoor closes, albeit slowly. Now it's on the glass but not moving up the glass, sticking real low along the gravel line. It's eating because it's mouth is going but it's barely moving. I have 3 other nerites in my 10 gallon who are all super active and were active within a few days of placing in the tank. anything to be concerned about?