Clindamycin Hydrochloride and stomach upset

This was given to me for a periodontal (tooth/gum) infection. I've never taken this antibiotic before. Beside the normal (antibiotic) stomach upset and diarrhea, it was as if I was taking sleeping pills every 6 hours and generally felt like I'd been dragged behind a horse. 5 days into the medication, I started seeing flashing "crescent" lights in my vision. Needless to say, that was disturbing. It lasted for about 20 minutes before the "flashing" slowly moved to the left of my vision and then disappeared. That was a day ago and I only have 2 pills left which I will now take at 12 hour intervals. I've taken antibiotics over the years and never experienced this type of reaction. Needless to say, I will not take this particular medication again.... For the record, I'm a 62 year old Male.