What is the Past tense and past participle of sick?

The verb "sick" doesn't have a past tense or past participle. It's an adjective, meaning "ill" or "feeling unwell."

To express past sickness, you'd use the verb "be" (or "feel") and the past tense of the adjective "sick":

* Past tense: "I was sick yesterday."

* Past participle: "I have been sick all week."