John McCormack hit a car before carrying on with the damaged lorry on the A9 between Blair Atholl and Perth.
He drove on oblivious to the trail of damage he had left until he was finally stopped by police.
Perth Sheriff Court was told that McCormack could offer no reason why he drove on the wrong side of the road.
Depute fiscal Stuart Richardson said motorists were heading north near the House of Bruar shopping complex when they saw McCormack heading straight for them.
He said: "To their horror they saw the lorry coming south. He was on the wrong side of the road. They managed to get off the road onto the verge.
"The lorry missed them, but unfortunately it continued on and a couple with three children in their car weren't so lucky. He hit the offside of their car and scraped along it."
McCormack, 46,  from Kilmarnock, admitted driving dangerously on the wrong side of the road on 11 April last year.
He admitted failing to stop after an accident, and driving a vehicle which posed a danger because of the state it was in. A charge relating to cannabis was dropped by the Crown.
Solicitor David Holmes, defending, said medical investigations had taken place and McCormack had decided to stop driving in the wake of the incident.
Sheriff Fiona Tait deferred sentence for clarification of the medical condition and imposed an interim driving ban on McCormack.
A trucker drove on the wrong side of a major trunk road for 30 miles, forcing other motorists to swerve to safety, a court heard.