503 error on WordPress

I just had a big problem where after saving the updates I made to a page, the website started showing me a 503 error. The biggest error on my part was that I had not taken a backup of this website. :/

One thing that I have noticed many times in the past is that if the live preview in the Avia Builder stops working (does not change on changing content etc), the page definitely leads to an error after updating. In the past, this led to errors that could be redone by moving to a previous revision of the page.

But this time I am just getting a 503 with no access even to the GUI WordPress dashboard (so I can’t revert any changes). I opened up PHPAdmin to see if I could perhaps change something directly from the DB but for some reason the page that I created today has a creation date of 20 days back, so I decided not to touch the DB entry for now.

The main error that I am getting repeatedly is “Unable to allocate memory for pool”.

I don’t understand what went wrong. Another website in a subfolder on the same domain is working fine, so I don’t think this is a hosting issue. I use a shared Bluehost hosting, btw.

Please suggest ways to fix this.