can't think straight
to have difficulty thinking clearly, for example because you are too tired, too busy, or because a lot of things are happening around you

[TahlilGaran] Dictionary of Contemporary English ▲

confused unable to understand what someone is saying or what is happening:
I was rather confused by his question.
She gave me a confused look.
With the huge range of computers on the market, it’s easy to get confused.
She felt hurt and confused when her husband left her.
puzzled (also perplexed formal) confused because you cannot understand something, especially because it is different from what you expect:
The doctor was puzzled by the man’s symptoms and ordered several further tests.
He had a puzzled expression on his face.
Ross looked perplexed when the audience laughed.
baffled very confused and unable to understand something, even though you have tried hard for a long time:
Detectives admit they are baffled by the case.
a baffled expression
bewildered /bɪˈwɪldəd $ -ərd/ very confused and surprised when something unusual and unexpected happens to you:
He was bewildered to find three policemen at the front door.
Bewildered train passengers watched as the man was arrested.
At first she was bewildered by all the noise and activity of the city.
bemused /bɪˈmjuːzd/ confused and surprised by what has happened, or by what someone has said:
Local residents seem bemused by the sudden arrival of all the tourists.
She told him to leave, but he just sat there with a bemused expression.
can’t think straight spoken to have difficulty thinking clearly, for example because you are too tired, too busy, or because a lot of things are happening around you:
I can’t think straight with all this noise going on.

[TahlilGaran] English Thesaurus ▲

can't think straight
if you can't think straight, you are not thinking calmly and clearly about something.
I was so tired I wasn't thinking straight any more.

There are so many people talking, I just can't think straight.

[TahlilGaran] English Idioms Dictionary ▲