~WHAT IS UPSETTING OUR MELE?~

This is Mele. Pronounced May Lay. Not that it matters..anyway. There seems to be a problem. Doesn't she look healthy? Bright eyed..happy? Well, for the past two nights she won't come to bed at night.
She has slept at my feet since she was 6 weeks old. Night before last when I put her to bed, I lift her up as the bed is too high, or so she says :) she began acting like she saw something..jerking her head this way and that..watching something I couldn't see. Then like a shot, she was off the bed and gone. I looked around..saw a little fly on the ceiling..and killed it, then went and got her and put her back on the bed. The minute I walked into the bedroom with her, she began shaking and her heart was racing. She..is not..a nervous dog..a yapper and normally very brave. Too brave. How could it be that tiny fly that frightened her as they are usually something she playfully chases?! Now here she was squirming to get away so she could run..and she refused to return. All night long.
Last night...same thing. Exactly. Acting like she sees something..and streaking from the room and refusing to return. Heart pounding, shaking and strugging to get free and run. Three times I carried her back, spent time talking soothingly to her, held her (not easy to do) and tried to just calm her obvious fear. Nothing worked. She was gone exactly as before when I loosened my grip. I finally gave up..couldn't sleep and was now wide awake. I blogged, unsuccessfully, played scrabble until nearly 3.
I finally was able to get to sleep. I slept late.. and this morning, though she did not come into the bedroom..she jumped into my lap the moment I sat down in the living room and kissed my hands and face almost apologetically. I am mystified. What is she seeing and what is spooking her?? She is obviouisly watching something..what?? Is she hearing something I cannot hear.
Being in California and living on top of a fault...that entered my mind but T looked at me like I was losing it..so I let that one go. :) Any idea's? I hate having her upset like that and I miss her at my feet! I can see one night..but not two. What could it be?