when I was aslept I saw a dream that it happened in the nextday

I have problem with tense I need more practice but its defficult to make sense

You can simply say;

" I dreamt last night, and it happened today."

I used 'dreamt' because the action was already done last night.

I also used 'happened' because the action already happened beforehand.

I didn't use happen only, becuse even if it happened today but it already happened this morning and you already conclude that it already happened and you saw the same thing it happened in your dream.