I find with writers block it is more the venue than actually a block...when this happens I head to the river bank and tranquility and things start flowing again.

As to what Gordon mentioned about inserting points to revisit.....the brain goes faster than the keys on the keyboard and fleeting thoughts can not only be lost but also interfere with the flow of the idea or words that were in motion at the time the thought pops in....even breaking away from the idea to key in a point can break the flow...to circumvent this when writing, I have a voice recorder in voice activation mode, and I just speak the thought that popped in, and then can revisit it when I am done what I was currently keying in...works for me. (as a single parent, the kids were told that if the keyboard was clacking then no interruption until it stopped and then they could have my attention....very hard to get the flow of an idea back - wording the way you wanted it - if interrupted midstream)