What causes sudden erectile dysfunction?

I'm a 23-year-old guy who isn't sexually active (I know, I know), but I do masturbate regularly.  Up until a few weeks ago I was getting erections every five minutes, and even after ejaculating, I would be hard again within minutes.  Today, however, I was looking at pornography on the Internet and no matter how much of it I saw, I couldn't get an erection.  I've been masturbating more frequently lately, due to boredom, and I was wondering whether that might cause it.  I've also noticed that the veins on my penis look a lot darker than they used to, which I'm guessing might indicate a blood flow problem.  I just can't understand how it happened so suddenly.  Will it get better on its own, or do I need to see a doctor?

[metropolis]

Well, moderation is the key to a happy life and that includes masturbation, too. Masturbation is normal and safe, but why overdo it?

I'm sure there's nothing wrong with you. It's perfectly normal to fail every now and then or go through periods of lower libido; ED only refers to the PERSISTENT inability to obtain or maintain a penile erection. Anyway, if the situation persists, don't be afraid to go see a doctor (urologist), but, again, I'm sure you won't need it.