Weird body sensations are just part of PTSD. My therapist tells me to honor them. I like that, it is better than freaking out about them.
For me, I get the sensation that there are literally holes in my head or frozen parts that do not work. It is disturbing.
She tells me to pay attention to the sensations and put my hands on the location they are occuring. It does help. If I place my hands on my head when it is feeling holey or floaty and just keep them there, eventually the feeling of warmth from my hands is noted and that helps ground me.
I think with PTSD you become so used to feeling outside your body that the sensations of being outside your body become prevelant. Paying attention to those times, what made you feel that way, and taking steps to alleviate those feelings all help.