Mine do that all the time, and none have taken the plunge and committed suicide! I used to try to take them off and move them down the glass, until I got tired of it! They are just looking for algae, and will move back down the glass when they get tired of that spot. They can move rather quickly when they want to.
Some snails are tidal snails, don't know about these though..... they're used to spending extended periods of time out of water until the tide comes in again.
My smaller snails do that all the time. Sometimes I think they know my CC star won't get them up there. HAHA. All of my snails have made it and they stay out of the water for significant peroids of time too.