After rebooting my laptop (which shut down probably because of low battery), I found out that Opera has deleted all my extensions and bookmarks, and also the fancy sidebar is no longer present.
The history IS NOT deleted, and I DID NOT use any 'cleaning' software. Fortunately I can copy the bookmarks from another browser, but I've spent hours searching for extensions and picking those most suitable for me so I would be very frustrated to find out they're gone for good.
Running Opera 49.0.2725.47 on Windows 10.
Thanks for any help.