I sometimes have a similar feeling to you with my sense of self but rather than an expansion into infinity, it was a shrinking of my "soul" or a shrinking of me the viewer and letting my body do the outside world experiencing. It's like I retreat into a tiny control room in my brain where nobody can see me or hurt me and I let my body do the work of experiencing things as I watch. It's kind of similar in that my body becomes one with everything and my self shrinks so much that it's nothing.