Is it normal to suddenly feel low and melancholy?

I couldn't sleep last night, so I decided to drive out to the coast. When I stopped my car at the top of a cliff and looked out at the city I suddenly felt deeply sad and guilty, similar to the feeling of loss or grief and started weeping. I'm an extremely unemotive guy, so I shocked myself a little. But I couldn't really help how I was feeling. I'm fine now, but looking back I don't think I've ever felt so unbelievably dismal in my life. I don't really know what happened then; I just wondered whether or not it was normal to suddenly feel like this.