For the past week my one eye goes into an involuntary, spasmodic twitch. What can this be?

Eyelid twitching. Eyelid twitching is often due to any cause of eye irritation, stimulant use, stress, lack of sleep, neurologic disease, and other issues. Try using frequent artificial tears, getting adequate sleep and minimize stress, and stop stimulant use. If this persists, see an eye doctor.