My normally fearless DS (2 1/2) has very recently developed two very severe fears.

He is suddenly terrified of public washrooms.  He is fine at home and at friends houses, but if I take him to the mall or the grocery store or a restaurant he screams bloody murder if we have to go into the bathroom.  He tells me that he is scared of the potty.  I have some idea of where this might have come from.  Some public washrooms have those self-flushing toilets that literally "suck" the water down in record time, and some have those extra-strength hand driers that sound like a jet engine, and I imagine that maybe one of those sounds caused this sudden fear, even though he has been exposed to these sounds since he was born. 

However, around the same time as the fear of public washrooms came to light, he also because terrified of the dark... and I do mean terrified!  The first time it happened was in the middle of the night, he woke me up screaming and I ran to his room.  He said there was a monster outside his door, and he was shaking so hard it took me almost 15 minutes to calm him down.  I lay with him for about 1/2 hour but he wouldn't go back to sleep.  I finally told him I would leave his door open and the light on and that's when he managed to settle back down.  Anyhow, since then he refuses to sleep with his door closed and the light in the hallway must be on.  I have no idea what triggered this.  He has always slept with his door closed and he has never needed a night light.  

Would you be concerned if your child suddenly became fearful of things that never bothered him before (especially if there were no incident, that you could recall, that might trigger that fear)?  I'm more concerned about why he would be afraid of these things, rather than I am about dealing with the fear (I'm sure that with positive reinforcement and a lot of patience, we'll manage to help him overcome them).