She lay in bed, contemplating.

她躺在床上冥思苦想。

《牛津词典》

She lay in bed looking frail.

她躺在床上，看上去很虚弱。

《柯林斯英汉双解大词典》

Pillar lay in bed, unable to speak and know anybody around.

皮勒躺在床上，说不出话来，也不认识周围的人。

youdao

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

VOA: special.2010.02.11

Babe Ruth loved children. In nineteen twenty-six, a child named Johnny Sylvester lay in a hospital bed.

VOA: special.2011.03.27

Brown lay in a bed in the courtroom throughout the trial.

VOA: special.2009.07.02

Now completely awake, she lay in bed, agitated, wondering whether she should risk another pill.

NEWYORKER: Shauntrelle

He lay in bed with only his face outside the covers, making clouds of vapor.

NEWYORKER: The Maserati Years

Nava lay in bed in the corner of their room, hiding under the blankets.

NEWYORKER: Waiting