Battery completely drained 70% overnight

Disable bluetooth connection to your phone, you might make it until you get home. Then search this forum, there are multiple possible fixes mentioned.

I always have bluetooth off unless I'm actively synching. It's at 0% and will shut down almost immediately, so no chance of using it even as a dumb watch for the next few days unfortunately. 

I haven't seen any applicable fixes, it seems like most related posts mention turning off features I already have turned off. Hopefully resetting once I'm able to charge will fix it. 

I keep looking at my wrist for the time and becoming annoyed, I've worn a watch every day of my life since I was 5 

Is it possible that something was in contact with the touchscreen overnight and kept the backlight on?

 It was in sleep mode, so the touchscreen was off, although it still might be possible that some of the buttons were pressed by a weird wrist angle or something. I did wake up a couple times in the night and didn't notice the backlight on though, so seems unlikely. 

UPDATE

I got home and fully charged, then double checked all the settings (bluetooth off, pulse ox manual, etc) that have been mentioned in regard to battery life. I also changed the heart rate monitoring from 'smart' to '1 second' based off of the heart rate accuracy thread.

i don't know if it's a semi-reset from the battery drain, or if the smart heart rate was causing an issue, but my battery drain is better than ever now. It's the same usage pattern as before my trip and has only used 4 days worth of batter in the last 5 days since the full charge. Hopefully this continues!

There is no „smart heart rate“. 
This option does only affect activities and how often the data (of all sensors) is written into the workout file. 

It does not change anything in the smartwatch mode. 

I mentioned it because it was the only settings change I made, it's always possible that something in the firmware is changed in unpredictable ways during an update

I tend to do a power cycle every now and then. Especially on long charges, eg from 50 to 100%.

Seen it more than once the battery would just drain for no reason. When travelling there's always a Garmin cable in my bag, even when just 1 or 2 days away.