Coco is such a sweet and happy go lucky girl, but sometimes I think she is bi-polar?!?

Happening noticeably more frequent, she will be laying down on her bed on the floor, or in bed with us, just growling. Head laying on a pillow, our arm, or just resting on her feet, just growling. What the heck?!?!

Sometimes the growl will progress to a bark. Just one single bark, she does not have a barking fit, but she growls....growls....BARK! growls.... and this can sometimes happen for 10 seconds, or 5 minutes!

I just don't know what is going on with her. On occasion I can tell she is growling and barking at something she is scared of, like last night I took her to my cousin's birthday party and she is not used to the noises in their house, she would yap at that and I could tell she was a little stressed out and scared.

It just seems like at home she does it for no apparent reason and it is happening at least once to twice a day, sometimes more.