Hey guys. Is it acceptable to mix present and past tense in fiction and dialogue? Here's a snippet of what I'm writing: "You should really lock your door." With a concerned look, he added "I've been telling you this since that robber incident". "Which one? I lost count." She said jokingly, sitting back down on the bed. "I don't want anything to happen to you, that's all." Would "sitting back down" be okay, or should it be "and sat back down"? I know this is a really oblivious question — I'm not a writer, don't hate on me!