When Did You Take Them

A Deny man staggered into the casualty area at Altnagelvin Hospital.
'Help,' he said. 'I've accidentally swallowed 200 aspirin.'
'Good grief,' said the nurse. 'When was this?'
'Friday night.'
'Don't be silly. Today's Monday so if you took them on Friday night you'd be dead by now.'
'Maybe it was Thursday, then.'