I can't be happy for someone if they have undiagnosed mental illness, no.
Being spiritual, religious, etc., is one thing. Most of my friends identify as Catholic or Christian, and many of my family members...particularly my mother...are very devout. They are happy in their faith and more power to them, my feelings about it aside.
That's an entirely different situation than those who report hearing voices, having literal visions...some people claim stories like they flew off into some world where Jesus was talking to them, etc. These things are signs...very sorry to insult anyone...of mental illness. So it's not that I'm making fun of these people that are suicidal, depressed, bi-polar, etc. On the contrary, I believe they deserve proper attention and not lip service. It's that I think it's medically irresponsible for their friends and family to say "oh that's nice that you talked to God last night" when something very serious is likely wrong.
Because if the "voice" today says :"thou shalt help the old lady across the street" who's to say tomorrow the voice won't say "jump off that bridge" or "drown your children?" And don't laugh, this kind of thing happens all the time.