grammar - “While she is sleeping, we...” – what verb tense comes next?

While she is sleeping, we decided to wake her up.

Trying to understand this grammar. Should we use decide or decided to?

Edit:

Okay, the reason I'm asking is because I'm trying to make some captions for a video. So the video will be

"While she was sleeping, we decided to...."

and afterwards we have another caption follows..

"Now she is awake..."

Using 'Now' usually uses present tense afterwards. If we use past tense earlier, it does not logically flows well with present tense later. So I don't know if I should use present or past tense.

Answer

While she is sleeping, we decided to wake her up.

That's simply wrong. You are mixing a present tense with a past tense. You could say:

While she is sleeping, we decide to wake her up.

This is pretty rare usage, though. In English we almost never give a narrative in the present tense. Present tense is primarily used to, (a) describe something literally happening right now. "Where is Bob?" "He is out to lunch." Or (b) to describe a continuous state. Like "Paris is the capital of France." It has been for a while and it is now and it probably will be for some time in the future.

More likely would be:

While she was sleeping, we decided to wake her up.

Also, when you have a conditional expression referring to a future event, you use the present tense, though logically you might think you should use the future tense.

WRONG: While she will be sleeping, we will decide whether to wake her up.

RIGHT: While she is sleeping, we will decide whether to wake her up.

(There's probably a name for this, it's not really the present tense, it's some kind of future conditional tense. But I don't know the name.)

Similarly:

If the stock market goes up, I can retire early.

Unless you stop acting irresponsibly, you will never get a good job.

Etc.