Feeling lonely among other people

I made a note some time ago about how I could feel lonely even when around other people. I wondered how I could feel this way walking down the street with hundreds of people around me? It felt like I knew too much about what could go wrong with life. I felt like other people's unhappiness was palpable. Like I could sense it in the way they looked, the things they said, they ways they acted. These days it's a complete turn around. I can't help but feel connected to everyone, even when I'm on my own in a crowd.