Even if a driver’s BAC is not at an illegal level, hangover symptoms could result in the driver causing a crash. The police might not be able to charge the driver for driving while impaired, but he or she is still going to be at fault for the collision.
In these situations, the at-fault driver’s hangover does not matter much. He or she was negligent and probably should not have been on the road in the first place. Your lawyer may try to use evidence of the at-fault driver’s hangover to bolster claims about other forms of negligent driving this person engaged in. Evidence of a hangover or drinking the night before makes it harder to dispute the driver’s negligence at the wheel.