Simon Steggall, 42, of Warboys in Cambridgeshire, said Dory, a one-and-a-half stone rabbit, jumped on his chest and thumped furiously when he passed out while watching television.
Dory's odd behaviour caught the attention of Mr Steggall's wife, Victoria, 32, an ambulance driver. When her attempts to bring him round failed, she rang 999 for paramedics for help.
"I work for the ambulance service and I'm embarrassed that the rabbit spotted it before I did," Mrs Steggall said.
Mr Steggall said his wife thought he had simply nodded off.
"When I have one of these turns I can't speak or move, but I can still hear
and I heard Victoria's tell Dory to get down.
"Although she is a house rabbit, she's not allowed on the furniture.
"The rabbit came up on my lap and started tapping and digging at my chest
and looking at my face.
"That caught Victoria's attention and she realised something was wrong."
Mr Steggall, a diabetic since childhood who has to inject insulin four times
each day, said he did not get any warning when he was about to be unwell.
"One moment I am vertical and next minute I am waking up with a paramedic.
It's like a flick of a switch."
The couple have had Dory, a three-foot rabbit, for three months, but she is not the first pet to respond when he has a diabetic reaction. Mr Steggall said he once had a black labrador who would cower in a corner when his blood sugar levels began to fall dangerously low - reminding him do a blood test.
