The iOS 8.0.1 update was supposed to fix a bug that prevented new HealthKit apps from working, but in the process it knocked out network and TouchID functionality for iPhone 6 and iPhone 6 Plus users.
"We have a workaround for you if you have an iPhone 6 or iPhone 6 Plus and you lost cellular service and Touch ID functionality today after updating to iOS 8.0.1," reads the statement.
It involves ensuring iTunes is up to date, connecting the affected iPhone to your computer, backing up your iPhone, downloading an iOS 8 file for iPhone 6 (here) or iPhone 6 Plus (here), and selecting the file by holding the Shift (on Windows) or Option (on Mac) key when clicking Check for Update.
Of course, that leaves you back at square one, with no operating Health-related apps. For this, Apple confirms that "We are also preparing iOS 8.0.2 with a fix for the issue, and will release it as soon as it's ready in the next few days."