Short post, but more noting this for myself more than anything. There are several times when I've blogged little fixes and they've proven handy to have in the future, e.g. when I'm setting up a new PC. Partly because I know they're on my blog, and partly because the posts are titled in the way I would search for a solution.
If you have a Windows PC (I think 8 upwards; but definitely 10, and 8.1) with BitLocker enabled, you may find that it reboots shortly without you even doing anything. If you've a long password and aren't a quick typist, you may even find that this means you struggle to enter your password in time. This is apparently a problem if you have a UEFI install, which will be a common configuration these days.
Having just tested this simple fix that I saw on Microsoft's forums:
bcdedit /set {bootmgr} bootshutdowndisabled 1
it seems to have resolved the problem; the password prompt will remain on indefinitely.