When you have an electrical problem the sound and RPM's typical change like someone flipped a switch, when it's a fuel problem the RPM's normally chnage a little slower and smoothly. It sounds like a coil failing from your description.
A leaking head gasket typically doesn't spray water anywhere and is not noticable from the outside, but it can force exhaust into the cooling water jacket, and depending on the size of the leak it may not allow any water to enter the block and you just see steam, or intermittent water flow with spurting and some steam.
