Getting Felix to sleep through - executive summary

So Felix is consistently sleeping through somewhere between 9 and 11 hours every night. He doesn't always go to bed easily, sometimes he wakes up in the middle of the night and needs to settle himself back again, and often it's nearer 9 hours than the desired 11 BUT the important thing of note is that I am getting decent kip, at last, and I think I've sort of stopped moaning about it. But it does beg the question - why do I still feel so tired?