Is the sleep and HR data available on the watch self? If not, then you might have activated the Battery Saver during the sleep. If the data is on the watch all right, then I recommend to Remove and Add a Device From the Garmin Connect App | Garmin Customer Support, wait till the next morning, sync, and see whether it helped. If not, then have a look at the Troubleshooting guide for (some) data missing after syncing for more tips.
