Why is my mixer not maintaining a consistent speed when turned on .

When I turned on the mixer today it initially began beating as normal but the speed of rotation began to intermittently slow down, then regain speed, but within a short time stopped completely. Following a rest it is responding to being turned on and will speed up but is not maintaining a consistent speed and I’m sure it will stop in a short time as above. I have no way of identifying the problem myself…can anyone offer suggestions?