Presently, Tokyo and Sydney are down more than a "mere" response in sympathy with USA. SP reflects that.
Tomorrow almost certainly will be ugly, very ugly. President has been on TV twice to reassure. Fed has injected the big dough. So what's left. Nada.
Hell, it's the credit inflation that is the reckoning here. Giving markets more credit at this stage is likely giving a boozer in a terrible stuper a shot of pure grain alcohol. The hangover's the bitch, and this one has not even started yet.