What explains a sudden voltage drop to laundry room?
This sounds like a “back stab” problem to me except you said 20 amp and backstabs are only approved for 15 amp circuIt. Current code requires a dedicated circuit. I would expect to find a loose connection or broken wire at the receptacle or in the main panel. If an older home with multiple receptacles on this circuit work backwards to the panel it will be the first not functioning receptacle or the last working one. 

What are you looking for? A loose or broken wire at a wire nut or screw since a 20 amp circuit. I usually find them in the receptacle boxes as the wire fill is tight there compared to the main panel, but it can be in the main at the breaker or the neutral buss.