I've had the same experience. I just look at my fabric, doodle in the sketchbook, and then walk away.
One thing that has helped jump start me is doing something small. Not to long ago a nonprofit I've sewn for was collecting doll quilts for a fundraiser. I was able to crank out three of them in a day or so, using some block ideas I needed to get out of my system. It was no stress, no pressure, and it got me out the starting gate.
The slump comes back, but taking baby steps seems to help get me out of it.
Laurie