Question

since i couldn't sleep i got up and went to upstairs-correct the mistake​

Answer 1

Since I couldn't sleep, I got up and went upstairs

Correction ➡I went 'to' upstairs... 'To' will not be there.

Hope it helps you:)

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Answer 2

This is not what most natives would say. Look there are two types of sentences: "grammatical" and "natural" sentences. A sentence that can be "grammatical" might not sound natural.

But as for your sentence:

I couldn't sleep,so I got up and went upstairs.