I’ve used a couple of iPhone apps and Apple Watch apps, currently using AutoSleep on the watch. It gives me stats similar to the ones phi shows for their app. I find some of them useful (the general sleep ratings match my feelings about how good a night I had; the sleep credit/debt percentage match how tired/energised I am through the day), some of them garbage (it gives a “readiness” rating when you wake up which bears no resemblance to how ready to get up I feel), and some of them are interesting data I can act on (consistency of bed/waketime). I’d like it to tell me more info about night time wakings but although there’s a sleep efficiency rating (% of time in bed you were actually asleep) it’s no actual use because I tend to give up when I can’t get back to sleep so I get 100% efficient for sleeping between 23:00 and 04:00 when really I’d rather stay asleep until 07:00.
I too have been searching for the magic correlations to get rid of headaches, I always feel that sleeping is most of the problem, but Exist’s correlations show me that lack of water the day before is actually better correlated to headaches. I think this might be down to the effects of lack of sleep being over multiple nights though which Exist doesn’t currently correlate against. I still think trying to sleep better has to be helpful.
My problem is that I have to keep a close eye on the data; because you’re wearing it in the day too it picks up naps well, but since I’m a restless sleeper it often thinks I’m awake when I’m asleep and also asleep when I’m awake (on the sofa with my laptop for example). It has calibration to deal with this and uses heart rate dips as well as movement but there’s only so much it can do for someone who sometimes moves more while asleep than when awake!
As far as actionable data go I’m trying to work on getting back to sleep quicker (or at all) when I wake up in the night and getting to bed in time to have a chance of staying in credit with the sleep bank. The second might be something I could beemind though I’m not doing currently, the first not so much.