I couldn't concentrate, presumably because I was so tired.

我的精神集中不起来，大概是太累了吧。

《牛津词典》

That night I was glad, because I was very tired.

那天晚上我很高兴，因为我很疲惫。

youdao

I meet my friends for dinner or I just go to bed because it's so late and I'm tired.

我和我的朋友们一起吃晚饭，或者我直接上床睡觉，因为太晚了，而且我很累。

youdao

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

VOA: special.2010.02.11

But let's not try and figure out what's going on with this big, big example because we'll get really tired.

但是我们不用去想,这个超大的例子是怎么运行的,因为那太累人了,哦实际上，在我们这么做之前。

麻省理工公开课 - 计算机科学及编程导论课程节选

And everyone at the office would get really tired because they don't have their caffeine.

没补充咖啡因，在办公室的每个人都会感到疲惫。

Let's 实战 - SpeakingMax英语口语达人

We never went far along the footpaths, because Tony tired easily.

NEWYORKER: Hand on the Shoulder

For the most part, one has to take the pope at his word: He's stepping aside because he's old and tired, not because of any particular crisis.

CNN: February 23, 2013 -- Updated 1735 GMT (0135 HKT)

Neruda bought the home in 1959 because he was tired of living in Santiago.

BBC: Chile through Pablo Neruda's eyes