Hi, @caporrimor
Welcome to the Canvas Community! Yes, that can be distressing, and I'm pretty sure I know what happened; it has happened to me as well. Fortunately, if my guess is right, it's an easy fix.
In Speedgrader, you'll see a vertical bar with three dots. Normally it divides the web page so that the student's submission appears on the left in DocViewer, and the area for grades and comments is in a narrower panel on the right. Clicking on the three dots displays the left panel in full page width. I suspect you clicked on that bar in error. You should be able to see it at the far right of Speedgrader (it's now yellow), and when you click on the three dots again, the panel for grade entry and comments will reappear.
I hope that does the trick! Good luck wrapping things up!
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