The As is possibly the worst card you could see, as it completes the flush draw and a lot of LAGs love to donk raggedy Ahi hands on dry flops like that. Of course, the LAG could also know this.

After SBs donkbet there are now 9.5BB in the pot by my count, which, to state the obvious, means you need to be good 9.5% of the time. This really has to come down to a read on the LAG and how much you've been folding at the table. I find donkbettors give me a lot of trouble so I'm always taking notes on what type of stuff people donk. Nevertheless, assuming the LAG isn't a complete maniac, I agree with the fold, because after you smoothcall the flop and raise the turn, the LAG can't think you're likely to fold anything. Of course, next time you probably should show down to avoid being exploited.