Stupid move or worthwhile gamble?

[Lottery Larry]

11-player tourney, second one of the night. 3 places paid 60/30/10% I'd won the first one catching some lucky boards to build a big stack that I could beat people over the head with.

Second one, my luck isn't as good. Some bad steal attempts, some unlucky flops have me down to about 15% of the starting T1500. The previous hand, I'd raised preflop with a medium pair, been called by overcards which hit the flop and tried to move him off on the turn, representing the Ace on the flop. He was determined to call me down with his second pair.

The hand in question- blinds are 25/50. Folded to me in early middle position with A7o and decide to move all-in, thinking the guy in the SB (who called me the last hand) would call me on this one with a lower hand. I was pretty sure that everyone else between us would fold (3 players). They did, he called, everyone else dumped, including the big stack to his left. He had QxJs, I held the 7s. Ace flops with 2 spades, another spade on the turn, river Qs.

Bad decision? The big stack was being aggressive against me with his 4x stack, so I figured I'd need to get chips in order to protect myself.