It USED to be insomnia. A few months ago, I started being able to reliably sleep through the night, after decades of being up 'til 2, 3AM on a regular basis. Then, after two *months*, I started getting insomnia again.
Wait, it gets better.
Now, I have intermittent insomnia. Three or four nights per week I'm fine, the rest I'm up half way through (check the timestamp, I'm on the east coast of the US, guess what kind of night this is!). And this is FAR worse than constant insomnia, because at least constant insomnia is reliable.