Dremel problem

[Acey]

Was cutting the side panel at third speed with my dremel multipro and out of the blue the thing starts spinning so much faster. Turned it off and tried first speed yet its still spinning like 6th speed. Is this a reaction due to overheat, surge, or its time to change a new one?

[Redundant]

Have you checked the motor brushes? (one on each side) These might need replacing but I'm not sure if this would cause the increase in speed.