note disappeared while I was writing

Hi elenapelaez,

Thank you for participating in the Apple Support Communities. We understand you're missing an important note. You can try recovering it on the iCloud website. This article has the steps: Delete and recover notes on iCloud.com.

"Recover recently deleted notes

You can recover and edit notes you deleted in the last 30 days on iCloud.com or on your devices that are signed in with the same Apple ID. However, you can’t recover notes you permanently removed.

1. In Notes on iCloud.com, select Recently Deleted in the folder list on the left.
2. If you don’t see Recently Deleted, you don’t have any notes in that folder, and there’s nothing to be recovered.
3. Select a note, then click Recover in the Notes toolbar.
4. The note moves to the Notes folder.
5. If you want to move a recovered note directly to a folder you created, drag the note from the Recently Deleted folder to another folder.

Note: If you delete a shared note that you don’t own, the note doesn’t move to your Recently Deleted folder. See Delete shared notes on iCloud.com."

Also, this article has some steps that may help as well: If you're missing notes on your iPhone, iPad, or iPod touch.

If you need further assistance, contact Apple Support.

Take care.