My Husband Was Driving And Had To Cover Up His

My husband was driving and had to cover up his left eye because he was having an episode of tunnel vision. He's a remodeling contractor and was headed to an appointment and had to cancel the appointment to come home and put a cold pack on the back of his neck and relax for a bit.
What causes these types of episodes?
For lunch he had "Carnitas" which is pork and took 1 prendensone for his sinus infection and wondered if the combination had any effect on this?