Sonny is over 100, and no matter how genetically strong someone's mind is, it's inevitably going to slip when you reach such an age. I doubt he really understands much of what his life was anymore, just recognizes faces and voices. It's also possible he's waiting for the right time to send Michael to open his hospital window so he can come up from behind and shove him out.

"...the successful annihilation of organized crime's subculture in America would rock the 'legitimate' world's foundation, which would ultimately force fundamental social changes and redistributions of wealth and power in this country. Meyer Lansky's dream was to bond the two worlds together so that one could not survive without the other." - Dan E. Moldea