Can I ask of any other suspected or diagnosed ADHDers - I read something curious in the "You're not crazy..." book about typical daily patterns of wakefulness, because it described me absolutely accurately.
This is the passage:
Some ADDers report that on a given day, their activity levels seem to
build from morning to evening. They are slow moving and thinking in
the morning, functioning well only if they can carry out routines without
interruption. Early morning conversations with family members
can consist of grunts and one word answers. These ADD adults describe
themselves as operating on "autopilot", capable of little more
than routine, automatic functions.
Nothing helps to speed up this process. These folk begin to gain alertness
by midmorning which is a problem when they work standard
daytime hours. By noon, they're going full tilt, using their energy to
talk nonstop to coworkers over lunch. With energy reserves drained
by mid-afternoon, the big slump often hits with a fight to stay awake.
The cycle often continues with a late afternoon shot of newly found
energy when they start revving up again. For many, the evening hours
are the most productive-late afternoon or evening shifts enable them
to work at peak efficiency
It is so true for me. Whether I've been to bed late or early, I really struggle to wake up in the mornings and am horribly grumpy and can't cope with changes to my routine. Weirdly when I have had less sleep I am often better.
By lunchtime I have energy and am ravenously hungry and want to do everything. But then at about 3pm I feel so tired that I could - and often do, if I'm at home - fall asleep, and then again it takes me ages to wake up. I intend to sneak off for 20 minutes and then DS is poking me saying "I'm hungry... where's dinner? It's five o'clock!" If I push through to when DH gets home and sleep when DS is in bed I can easily sleep until morning, but then I miss my evening, and often dinner. But if I try to push through to 8, 9, 10pm and have an early bedtime, I'm wide awake by then and don't want to go to sleep at all. Indeed, often when I go to bed at 10 or 11pm I am wide awake and find it really hard to get to sleep, easily disturbed by stuff like DH moving in the bed, noises outside, light, etc. I feel at my most attentive, focused and motivated and alive in the small hours of the morning. I have to set myself a bedtime because I can so easily lose track of time.
DH says to me "You should stop napping in the day, then you'd go to bed earlier and get up easier" and gets really irritated that I take over an hour to get out of bed, but I have tried doing that for several weeks at a time and it doesn't seem to stop the same cycle. And anyway, he often goes for a sleep after work. So you can see I was totally fascinated when I saw it written out like that, exactly as if they had seen a cross section of my life. Do others get this or am I just weird? 
I have recently found that if I exercise in the mid afternoons right when I feel sleepy instead of napping that boosts my energy immediately and carries me through to 11 but it's so counterintuitive to me to do something active when it's the last thing I feel like doing that I often can't face it at all or I just forget. I'm going to try and keep on top of that, though, I think.