A woman developed severe dizziness after standing 30 feet (9.1m) away from a cannon which was fired at a Civil War re-enactment.
The 37-year-old, who has not been identified, said her head spun so much she felt like she was 'on a carnival ride'.
She had developed a condition called benign paroxysmal positional vertigo after the gun blast knocked loose sensitive crystals inside her ear.
This then sent jumbled signals to her brain about which way up she was and made her feel dizzy when she moved her head, and also gave her headaches and made her feel sick.
Doctors in Ohio treated the woman using a simple manouevre which patients can do at home just by moving their head and lying down.
The woman, who has not been named, was standing around 30 feet (9m) away from a Civil War-era cannon when it fired at a re-enactment (stock image)
Before developing the dizzy spell, the woman, who was married and in full-time work, had been in good health.
But she developed vertigo after visiting a Civil War re-enactment when the cannon she was standing near fired a blank.
The explosion made her immediately dizzy, she said, but she assumed her sudden headache was a migraine.
When her head kept spinning over the next four days, however, she feared something more serious was wrong and visited doctors at a medical centre in Bellefontaine.
Positional vertigo may be caused when crystals in the ear are knocked into the semicircular ducts in the vestibular labyrinth (shown in the middle of the diagram to the side of the snail-like cochlea)
Benign paroxysmal positional vertigo is caused by problems with tiny organs in the inner ear losing the ability to accurately work out which way up the head is.
If sensitive crystals inside the otolith organs become dislodged and move into a different place in the ear, the brain tries to correct the position of the eyes at times when it usually wouldn't, such as when people lie down or lean to the side.
To treat vertigo at home, people can try the Epley manoeuvre – a simple series of movements designed to get the ear crystals back into a place where they don't cause dizziness.
For a problem with the left ear, people should:Start sitting up on a bed, with your legs flat on the bed in front of you. Turn your head 45 degrees to the left. Lie down, keeping your head turned to the left. Wait 30 seconds. Turn your head to the right 90 degrees, until it’s facing 45 degrees to your right side. Wait 30 seconds. Roll over onto your right