Sadness

At times it seems all should be normal now.  I can think, remember (or use tools to assist), feel, dream, etc.  All of the things a brain should be able to do.  And yet there is something in me that feels horribly dissatisfied.  What is it?  Failure, broken dreams, disconnection, or an inability to be satisfied.  I do not know what to call it.  I only know I feel on the brink of tears and feel  like I don’t really belong or matter.