Power out in part of the house

I was in my bathroom yesterday with the lights and the fan on. All of a
sudden the lights and fan go off. Only the bathroom I was in and part of
another room were affected so I assumed a breaker had been tripped. But
when I opened the fusebox none of the breakers had been tripped. I even
flipped the corresponding breaker just to be sure.

Can I safely assume that the breaker is probably bad and will need to be
replaced, or is it possible something else is wrong?