I have periods of time where I do feel this way, it was more often and lasted much longer (months, even a year or two) when I was much younger.
It is like having something between your self and the rest of the world, mine felt like a thin glass wall through which I can see and be seen, hear and be heard, but all in a muted, deadened manner, as if the 'glass' also had the same effect as acoustic tiles. Empty all around. The lack of pain is, I think, a protective mechanism. Feeling the empty is excruciatingly painful. During these times, many other people saw me as "aloof" at best "uncaring", or worse.