When AutoCAD closes unexpectedly (crash or end task) you may be able to recover some work after your last QSAVE. The Autosave file has a .sv$ file extension and is stored in your Windows temp folder.

Use the Drawing Recovery Manager to find the Autosave file. Usually, AutoCAD will detect that it was shut down unexpectedly and will open the Drawing Recovery Manager the next time you launch AutoCAD. Drawing Recovery Manager displays the drawing file you were working in when it closed as well as the backup file (.bak) and Autosave file (.sv$). Simply right-click and choose Open on any one of these files in AutoCAD. When you open the Autosave file it will be copied to the same folder as the original drawing and a .dwg file extension will be added to its file name.

When you have AUTOSAVE enabled you can specify how many minutes between Autosaves. Open the OPTIONS dialog, switch to the Open and Save tab to see where the Autosave and time between saves are set. By default AUTOSAVE is on and set to 10 minutes between saves.

Best practices advice.

Open both the original drawing (.dwg) and the Autosave drawing (.sv$) to compare these files. Run the AUDIT command to check for errors. Once you are sure you want to continue using the Autosave version of your drawing you can do a SAVEAS command to overwrite the original dwg after closing the original.

When you get a Fatal Error message followed by another AutoCAD Alert message you are asked to save the file.
Respond by clicking No.
Often when you choose Yes the file is corrupt and no longer usable.

Additional resources.

Read more about AUTOSAVE in the online help for AutoCAD.