Whose idea was it to show the Blue Screen of Death right after I saved nothing?

Good news is Windows writes down why it crashed, so you can find the cause instead of guessing. Here is how to read it, in order:

• Find the stop code. It appeared on the blue screen (for example MEMORY_MANAGEMENT or DRIVER_IRQL_NOT_LESS_OR_EQUAL). If you missed it, open Event Viewer > Windows Logs > System and look for an Error from BugCheck, which repeats the code and a hex value after the restart. Search that code together with your Windows version and you will usually find the common cause.
• Open Reliability Monitor (type reliability in the Start menu). It shows each crash on a timeline, with the app or driver that was running, and which update or install happened just before.
• Look at the crash dump. Windows keeps a small dump in C:\Windows\Minidump. A free tool such as WinDbg or BlueScreenView opens it and names the driver that crashed (often a graphics, network or antivirus driver). Make sure dumps are enabled under Settings > System > About > Advanced system settings > Startup and Recovery.
• Run the basic health checks as administrator: sfc /scannow, then DISM /Online /Cleanup-Image /RestoreHealth, then chkdsk C: /f at the next restart, and Windows Memory Diagnostic if the code points to memory.
• Update or roll back the likely culprit. Update the graphics, chipset and network drivers from the PC maker, and if the crash started right after an update or a new device, uninstall that update or driver in Settings > Windows Update > Update history.

If you post the stop code and the driver name from the dump, people can narrow it down quickly. Try to keep your work saved often until you find the cause, because a repeating crash on the same code usually means a driver or a failing memory stick.