Former company director Colin Farmer, 61, was hit in the back by 50,000 volt stun device and then handcuffed whilst on his way to met friends for a drink in his local pub.
Police had earlier been dispatched after reports of a man roaming around Chorley town centre in Lancs armed with a sword.
A patrolman spotted stroke victim Mr Farmer walking down the street using his white stick to get around and wrongly assumed he was the swordsman.
Today Mr Farmer who used to run an architect's practise said he had made a formal complaint and is pursuing legal action against Lancashire Police which has apologised and begun an investigation.
"The whole thing was like being trapped in a nightmare," said said Mr Farmer, a Fellow of The Instute of directors for 20 years. "I didn't even know the police were there. I heard this man shouting. I thought they were shouting at some people.
"I certainly didn't know they were police - and I certainly didn't know they were shouting at me.
"I thought I was going to be attacked by some hooligans. The next thing they fired a Taser at me, though I didn't know it was a taser at the time.
"I just felt this thump in my back. As soon as the taser hit me I hit the ground.
"I hit my head on the floor, then this policeman came around. I said 'I'm blind, I'm blind. I'm blind'.
"This policeman knelt on me and dragged my arms round my back and handcuffed me so tight I've had bruises since.
"I said 'you're hurting me, I'm blind' - and there's no way he could not have seen my stick on the floor.
"I walk at a snail's pace. They could have walked past me, driven past me in the van, or said drop your weapon.
"It's a sad excuse. They wouldn't even stop when I said I'm blind. I was absolutely terrified. I thought any second I'm going to have another stroke and this one will kill me."
Mr Farmer's horrific ordeal began at about 5.45pm on Friday. He was walking along Peter Street close to the Parmesan and Pepper restaurant when the incident took place.
After he was tasered Mr Farmer was taken to Chorley Hospital for treatment and was later released.
He said the explanations police gave him for their actions was that they had received reports of someone wielding a Samurai sword.
Mr Farmer has suffered two strokes - one in November 2008, and another in March this year, when he spent two month in hospital.
Chief Supt Stuart Williams, of Chorley Police said the matter had been referred to the IPCC, adding: "On Friday evening we received a number of reports that a man was walking through Chorley armed with a samurai sword.
''A description of the offender was circulated to officers and patrols were sent to look for the man.
"One of the officers who arrived in Chorley believed he had located the offender. Despite asking the man to stop, he failed to do so and the officer discharged his taser.
"It then became apparent that this man was not the person we were looking for and officers attended to him straight away.
''He was taken to Chorley Hospital by police officers who stayed with him whilst he was checked over by medics. They then took him to meet his friends in Chorley at his request.
"Lancashire Constabulary deeply regrets what has happened. We have clearly put this man through a traumatic experience and we are extremely sorry for that.
''Officers have remained in contact with him and his family over the past few days to enquire about his recovery and we will continue to keep in touch with him and keep him informed of our inquiry.
"We have launched an urgent investigation to understand what lessons can be learned and the matter has also been referred to the Independent Police Complaints Commission."