C172 pilot reported feeling fatigued; closed eyes for a few moments to recover with autopilot on; but fell asleep and violated a Class Bravo airspace.

Narrative

I was enroute from ZZZ1 to ZZZ2 in a Cessna 182. About 40 minutes from my destination at a cruise altitude of 7;500 MSL on the autopilot I began to feel a small amount of fatigue. I felt that if I could rest my eyes for a moment that would be okay. I fell asleep almost immediately. I awoke 30 minutes later inside the outer ring of ZZZ Class Bravo airspace.I immediately performed a 180 turn and exited the airspace; descended outside the airspace and proceeded to ZZZ1 which is my destination. I did not have clearance to enter Class B airspace.As a professional pilot I take this event very seriously. After some introspection of my errors I have identified two areas that need to be improved upon.My process for determining fatigue levels needs to be modified so that I have a greater awareness of my fitness to fly. In the future I will land the plane at the nearest suitable airport when I feel the need to 'rest my eyes'.I was not using any TRACON services such as VFR flight following. This omission was an unnecessary risk especially as I approached a busy airspace. I will use some type of radar services whenever available.