My hermits have burried them selfs but are still moving around.?

My hermits have buried them selves under the bedding in their tank and haven't come out. They have been under their for a while now and are moving around. Does it mean they are ill or starting to molt? I I'm worried and i want to know if they can be pulled back up to the surface. I am just scared if they are molting i don't want to touch them, if they are sick and don't want to come out, or if they are just under there hiding to keep a certain body temp. I just don't know.