Lets just say they have a quite, uncommon fear. Comments for Fear of the movement / rotation of the Earth. What is this phobia? This actually makes them suicidal and I feel bad How can I help them?
I've poked around online a bit, and to be honest, casual searches aren't turning up any identifiable terminology to describe such a phobia, which leads me to suspect that it's not officially recognized by psychologists. However, it sounds like your friend's anxiety is very real, especially if they are at risk of hurting themself. I would highly recommend talking to a parent, school counselor, or someone else who would be in a position to get your friend some professional help. That may be all you can really offer at this point, but it's important to make sure they have that type of support.