AJ Jordan at
I've noticed I tend to get sad when I'm tired. thinking I might hack up an Android app real fast that lets me easily record samples all day so I can do some real analysis.
There are some apps already that can help.
Look for Tickmate, Loop Habit tracker or Diary in F-Droid. Also look for “track” and will find some more.
In the F-droid archove there is also “Migraine Tracker”. It can be used to track “episodes” (migraine or whatever) in a very easy way.
Maybe you can revive it or fork it and update it easily to avoid the vulnerabilities that made them fall down from the “normal” archive.
https://f-droid.org/wiki/page/com.rhiannonweb.android.migrainetracker