So you would say in the past tense "I lay on the bed because I was tired."

VOA: special.2010.02.11

Everything that we had thought that Milton was telling us in the lyric present -- telling us directly, now -- suddenly gets shoved back into the narrative past: "thus sang the uncouth swain." The past tense is important there.

我们想过的弥尔顿在这首抒情诗里,直接告诉我们的所有事，现在，都突然在过去的旁白中一涌而现了：,“吟唱着粗鄙的青年人“，这里的过去时态很重要。

耶鲁公开课 - 弥尔顿课程节选

So can be changed slightly, depending on tense, past, present or future as well as whether or not you want to ask a question.

因此这个句型要根据不同的时态，如过去时、现在时和将来时，作出一点调整；另外也会根据是否是问句而略有不同。

There is 课堂 - SpeakingMax英语口语达人