What does this mean?

When I'm standing close to a tall ledge I'll get this overwhelming thought to jump off. It's a physical urge.. or If I'm driving down the road going fast I'll get this horrible physical urge to jump out or wreck on purpose. Just things like that. I dont want to die or kill myself but I get these horribly strong urges to just do it. Why??? How do I get it to go away? I'm scared one day itll take over and I'll actually hurt myself.