It's real, and I have experienced it. It also very painful, as [link] (anapests-and-ink) said. One time I was trying to think of a title, and I could not for the life of me come up with one that fit the writing. So I was pacing around my room, in the dark, CRYING thinking that I wasn't a good enough writer because I couldn't think of a stupid TITLE! So, yes, it is real.
I don't get writer's block, or at least, not as what most would think of as writer's block. I often want to write, but don't have anything to say or write about, which isn't really the same thing. Other times I simply don't feel like writing, but I wouldn't call that a blockage.
In other words, I'm not sure how to answer this question I do believe it's a real thing, but it's not something that's ever affected me personally. So I can't really answer either way here.