Well, for what it's worth there's an extra bit of info.
I can minimize the problem if I flex my muscles at diagonally opposite sides of my body, i.e. left leg + right arm and vice versa.
If I squeeze my right hand into a fist, I get a strong pulse on the inside of my left elbow. Figure that out. I can't.
I know. This all sounds weird, but it's also very disturbing. I have to go through this every night at the moment and it's stopping me from sleeping.
I wonder if this is the right forum...?