Wǒ zǐxì huíxiǎng le yíxià, hǎoxiàng quèshí jiàn guo tā.
I thought back carefully, and I think I did meet him before.
Tips
usage
回想 focuses on actively trying to recall something, while 回忆 (huíyì) is more about reminiscing or the memories themselves. 回想起来 (now that I think back) is a very common sentence opener.