Great Apes: You Wake Up In Your Lover's London Flat And Freak...because she is a chimpanzee. Paramedics and police arrive who are also chimpanzees but manage to talk you down - yes they speak impeccable English - and sedate you. When you come to, you try to explain that you are human only to find out that some humans are kept in zoos and don't use language and they are cnot at all bright. You've clearly had a complete psychotic break.
Will Self's "Great Apes" will leave you questioning what it means to be "human" at a very fundamental level. If it helps - and it pains me to draw the parallel - think of it as a thinking person's version of Planet of the Apes.