I upgraded my old windows to windows 10 when it first came out, and repartitioned my Yosemite mac drive to allow a larger pc drive after the fact. It was all working, and I could hold down the option key and see my windows drive and boot to it and all ran fine. I could not see the pc drive in start up disk on mac side, but I was ok with that. I was attempting to boot from a usb stick into a linux machine, but had messed up on the boot stick and it failed to load as the startup disk. I powered down the mac and restarted. When I restarted my mac holding down option I saw my mac drive and my efi boot drive but no windows drive anymore. I ran sudo fdisk /dev/disk0 and sudo gdisk -l /dev/disk0. results should be attached to this post. It appears that my drive dumped 83 gb of its partition as I have that much free space listed on my drive. Not sure how it happened. I am traveling and really don't want to have to reformat and start the bootcamp process over. Besides I really don't want to have to reinstall everything on the pc side again. Please hope someone can help.