I have a USB Bluetooth adapter on my PC which works fine, apart from after my PC is woken up from sleep or suspend - and then my Bluetooth is turned off untill I manually turn it back on again. There are plenty of fixes on google which involve setting kernel command line parameters, or module parameters to disable btusb.enable_autosuspend and usbcore.autosuspend but none of them fixed the problem for me.
What I ended up having to do was set the AutoEnable=true option in my /etc/bluetooth/main.conf. This means that when any new adapter is detected it will automatically be enabled. The option should already be in the file but commented out.

# AutoEnable defines option to enable all controllers when they are found.
# This includes adapters present on start as well as adapters that are plugged
# in later on. Defaults to 'false'.
AutoEnable=true

I guess my problem was that the USB Bluetooth adapter was losing power completely when the PC went to sleep, so it acted as if it was unplugged and plugged in again. This makes sense since the Bluetooth adapter is plugged into the USB hub on my monitor. I am using Slackware64 15.0, but this is probably a common setting among most Linux distributions.