Gary Burns (28) wounded victims in a rapid rampage on December 29, 2018..
A judge at the High Court in Edinburgh was told that it was likely to have been a drug-induced psychotic episode.
Lord Turnbull told Burns: "You pled guilty to a series of attacks against six individuals, two of whom came to assist you thinking you were under attack."
The judge said: "The injuries involved for three of the victims were very severe."
Lord Turnbull said it was offending "of a most serious nature". He pointed out that the condition which has caused difficulties for Burns and for which he takes medication was drug and alcohol induced.
The judge ordered that Burns should be kept under supervision for a further four years.
Burns, who has previous convictions for assault, was only released from custody a few weeks before the spate of attacks.
Burns earlier admitted committing the six attacks which resulted in disfigurement to all of the victims.
He first struck at The Auld Vic pub in the town's Grahams Road and lunged at John Montague as he returned from smoking outside and struck the victim on the head with a knife.
He fled before turning on others in the nearby street.
David Cunningham suffered seven "rapid stabs" to the chest and stomach.
James White and Lewis Cunningham were then injured as they tried to come to Mr Cunningham's aid.
Grant and Gary Logan were attacked after they got out of a taxi. Grant was slashed to the face and neck and Gary was stabbed on the thigh.
Several of the victims required hospital treatment.
Burns, of Falkirk, was later traced to a McDonalds at a nearby retail park and a blood-stained knife was recovered.
Defence counsel Geoff Forbes said Burns had previously been assaulted and was paranoid about being attacked again.
Mr Forbes said that if Burns continued to take his medication then there was protection for the public.
He said: "He accepts responsibility for what he has done and he very much regrets what he has done."