Dil Gira Daffatan meaning

Dil gira daffatan, or dafatan as the credits write, means my heart fell suddenly, as Daffatan means suddenly, achanak in Hindi.

You can also find another usage of this word in Gulam Ali's famous Ghazal chupke chupke raat din, where he sings Khainch lena wo mera parde ka kona daffatan.. aur dupatte se tera wo muh chhupana yaad hai. He just suddenly pulls the curtain. :)