Unfortunately, Unity crashes from time to time, and there is no way to ensure that data never gets lost. For this reason, make a backup of your project folder on a regular basis, e.g. by duplicating it. Save the duplicated folder somewhere else, maybe on an USB stick. To save some free space, you could delete the Library and Temp folders in the backup folder.
If you cannot retrieve your project for some reason, you could download Rick’s project state of the current lecture via the link in the resources of the video. It’s not the best solution but at least you won’t have to start over.
Hopefully, this helped a bit.
And yes, saving is crucial. I’m so paranoid, my fingers are always near Ctrl and S and keep pressing the keys every couple of seconds when doing something important on my computer.