These are now quite normal in the field of SEO. I got a similar shocked when I was first handled by a project from one of my old clients, who is running an e-commerce store. Some one attacked that website in the same way and then they attacked by spam backlinking. You can check it here https://thebackvault.com/.
I have disavowed those spammy backlinks and now creating healthy backlinks in the replacement. Thankfully, my cloudflare responded well on time to avoid the extreme of DDos attack. You need to worry more, it is just a patch of down-fall. Make a strategy for it and just do that. Hopefully, your website ranking will go high again.