The very first words of Mohit Chauhan's song in Robot and you're bowled. Well, if you didn't get the meaning of Pagal Anukan, or precisely Anukan, here it is.
Anukan is nothing but two words anu (अणु) and kan (कण) joined. Anu means molecule and kan means particle. Hence, Anukan means molecular particle, or just molecule, while pagal anukan means molecules of madness as pagal is mad.