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》

I was so tired I went straight to bed.

我太累，径直上床睡了。

《牛津词典》

I was so tired I crashed out on the sofa.

我累极了，在沙发上就睡着了。

《牛津词典》

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

VOA: special.2010.02.11

So even though I was really tired in the first one,

所以，即使我第一次去真的很累，

来伦敦旅游的 - SpeakingMax英语口语达人

I was tired so I went straight to my hotel.

VOA: special.2010.06.12

Before the match I was so tired, I was scared about how I would start the match, how I could play against Del Potro.

BBC: Nikolay Davydenko takes ATP World Tour title in London

It took me an hour and a half to get up in the morning and then I was so tired I had to lie down again.

BBC: Organ donor series

I'm so used to feeling tired from training, so I was just lying there unable to drop off.

BBC: No place like home for triathlete Alistair Brownlee