Truthfully, if this only happened to you once in 3 years, you are truly lucky! Saving often is of course the key. I also use AstuteGraphics plug-in AutoSavior so that when I do get a crash, I don't really have any issues.
Sorry about this trouble. Is the issue related to a specific document? If yes, could you please share the document with us? You can upload it to the Creative Cloud (https://helpx.adobe.com/in/creative-cloud/help/share.html) and share the download link.
I must also inform you that file recovery can't be guaranteed with a 100% success. We'll surely try our best.
Hello miss Bali, I have a similar problem. But I don´t saved the document as .ai file, only in .pdf file, and then immediately turned off my computer. A few hours later when I opened the pdf file in illustrator, a window appeared showing that illustrator could partially read the file, an when I opened I lost most of the work, but in the thumbnail it seems that the file is completely there. what do I do? Please help me!