When i was about 17, there was a song on the radio at work that Sheila liked.  It was by Billy Joel and called 'The river of dreams'. 

In the middle of the night

I go walking in my sleep

but Sheila kept singing

In the middle of the night

I go riding my bike.

For about a month, she would keep singing the new lyrics she created, and laugh every time she sang it, telling the same story over, and over, and over, and over............... I think it is called Inane humour. Singing your own song, dancing to your own tune, laughing at your own jokes :) 

When she was poorly, it started to play again in my head.