Did you really just ask this? You've got to be kidding me. If you have to ask that question you're already feeling bad for doing it. Do not quote APA at this kid, Monkey, if he cared whether it was a natural impulse he wouldn't be asking about religion. And you're not considered mentally unhealthy if you don't masturbate, natural impulses and mental health are NOT the same thing. Listen, you are not going to hell for masturbating. Logically speaking, it's highly improbable. NOW, if you masturbate EXCESSIVELY, you have a problem which may or may not cause some...effects, religiously AND psychologically speaking. Especially if you're doing it and regretting it afterwards.
Ask your spiritual adviser. No one who hasn't been to heaven or hell can tell you that. All you can do is ask your church and find out what its beliefs are, and follow those. Though, for the record, people who don't masturbate are considered unhealthy, mentally, by the APA (American Psychiatric Association). It's a natural impulse, and something people have been doing since the dawn of time. Even some animals do it. So if your minister says it's bad and you slip up and do it anyway, try not to eat yourself up with guilt.