5 mth lab personality changes

Question
We have a 5 mth purebred yellow lab we got her at 8 weeks exactly. She is the "perfect dog" housetrained, crate trained, heel, sit, stay, fetch etc. She attended puppy daycare for socialization since 8 weeks. (5 days a week for 4 hours total)  All of a sudden within the past week she is afraid of the vaccum cleaner, and a dropped metal bowl. (both she wasnt afraid of earlier until this past week) She just seems to be a very timid dog now and she never was before. I waved my arms around her like if I were going to hit her and she didnt flinch. I was trying to see if she thought she was going to get hit. (thinking someone hit her because we never did) She just jumped playfully around and thought it was play time. She is also always on leash in the house and in the crate if we cant watch her. We do not allow her to get in touble since she doesnt have a chance too. She gets all 100% positive praise. I dont know what it could be, she was never afraid of anything. Any suggestions???

Answer
While such a fear stage is common at 4 months, I have no doubt that is what is happening now.  Don't force her, don't let things overwhelm her, and above all, don't coddle her.  That will only reward her for showing fear and train her to do so.  Instead, coddle the vacuum cleaner.  Go up to it and pet it and talk to it, ''Good vacuum cleaner!''  My one puppy worked out of his fear of ladies in broom stick skirts without me doing that.  I had my own fear issues to deal with if I did.

Mostly give her time to get through it.