Terrence Williams headed quickly back home to Seattle once the Celtics season was over. And while he’s hoping the club picks up its option on him for next season and he gets to return, the February acquisition has to be enjoying having his head in one city for a while. From the Guangdong Southern Tigers of China to the Celtics to the bench to a key role in the rotation for the last three playoff games, it’s amazing he hasn’t succumbed to whiplash. “It’s definitely been a whirlwind,” the 6-foot-6 Williams said. “One, I can’t believe it’s over. Two, I can’t believe it’s over. And, three, I wouldn’t trade it for nothing. “Everything that we went through — everything that I’ve been through up to this point — I wouldn’t trade it.” Williams did not have an enjoyable experience in China, and with doubts about his attitude and approach to the game over here, there was room to wonder when his next NBA opportunity would come. After stops in New Jersey, Houston and Sacramento that didn’t work out as he would have liked, he was hoping simply for a chance. The Celtics needed someone who might be able to play some point guard, and it didn’t take long before Doc Rivers was saying that is his natural position. After some decent flashes in the regular season, Williams was jettisoned to the deep bench in the playoffs before the coach reached for him after getting down 3-0 against the Knicks. Now the chances of the Celts keeping him through the Aug. 1 deadline in his deal seem far greater. “I really don’t pay attention to that,” Williams said. “Before the Celtics, I always just wanted to make a point when I play basketball for people to watch and say, ‘Why ain’t he on the court? He can help us.’ “I think in the playoff games I was in, I’ve done that. So I think I can help the team. I definitely do. “I think I’ve grown up — a lot — in the past couple of months. I’d be happy to be here . . . of course.”