Sorry to hear that.
Unfortunately it is very easy to select all the item on the page by checking a box, and then hitting the delete button will delete everything.
You may be able to find some of the most recent items you looked at by going to your Recently Viewed list:
https://www.ebay.com/mye/myebay/rvi
Other than that, you may have to try to recreate some of your past searches to find the items you were watching once again.
If you go to the Advanced Search page, clicking on the empty search keyword field should reveal a list of keywords you have previously searched in your current browser.
It may also be possible to find past searches using the autocomplete feature of your browser by starting with a current search, then deleting some of the search URL and seeing what other URLs your browser provides as suggestions.
