The group I'm in taught me not to ask "is this normal?" But to ask "is this healthy?"
Among the group you're asking (a bunch of people with mood disorders), suicidality is pretty common and I'd say isn't particularly abnormal, but does that really matter? It's unhealthy, that's for sure, and any unhealthy habits (for lack of a better word) need to be addressed.
I'm sorry to hear your son is struggling and I hope he feels better soon.