Blow your mind
Expand your mind by use of hallucinatory drugs.
This expression became a commonplace saying and slogan in the 1960s hippie era. The first exact reference to 'blow your mind' that I can find is from October 1965, when it appeared in Ohio newspaper The Sunday Messenger - in Jack Thomas' Music Guide Top Ten:
"Pick Hit of the Week - Blow Your Mind - The Gas Co."
Slightly earlier, in the same year, Bob Dylan used 'blew my mind', which is effectively the same expression, on the March 1965 album Bringing It All Back Home, in his song Bob Dylan's 115th Dream:
A pay phone was ringin' and it just about blew my mind
Whether Dylan coined the term or repeated something already on circulation isn't clear, although it he was exceptionally creative lyrically at that period and his inventing of it is entirely plausible.