I feel like it's caused by when you get bored of how you're drawing, and you need something completely new and different out of your comfort zone to excite you all over again. Or maybe it's not even just being bored with how you're drawing, but the things you make don't make you happy anymore, or they start to infuriate you because everything you try making just doesn't come to any sort of self-satisfaction.
So over the summer, I was able to throw my art block out the fire escape by using a bunch of mixed media techniques; gouache, pastels, brush-inking, etc. I would think of what emotion would be coming to mind or which direction my hand feels like it should go instead of my brain telling which direction my hand should go in.
This was the start of it, inspired by Masha
Silly sketch of a forest-demon stick-doll thing Alex made