My shabumpkin

I have a 2 shabumpkin fish and a snail in a 40l tank (excus spelling mistakes) and one of the shabumpkins has suddenly started to not eat and lay at the bottom of the tank alot and I dont know why and I begining to worry. My fish I have had for around 4 years and they have never done this before but the snail I have had for about 2 weeks. Can you please help I am really worried about what is wrong!