Why am I feeling so knackered?

So. I was feeling reasonably good 3+ weeks ago. Legs felt strong, plenty of energy.

I then went on a 2 week mountain bike holiday in the Alps - first week was fairly brutal (practice and qualifying for a DH race), second week was just riding great singletrack in great surroundings. Very little in the way of pedalling done, but a good upper body workout all the same. Riding really well. Had a lot of fun.

Since I've come back, I've felt like utter sh!te. I'd expect the first couple of days of commutingto be a little rough until I got used to pedalling again, but I just feel constantly lethargic and my legs have no spring to them. The 10mile a day commute has been drudgery, I had a day off on Saturday, managed a decent 6hr xc ride on Sunday, but I'm still feeling that now. Went out early this morning for a Richmond Park road blat and was way off my normal pace. I was also very groggy when I got out of bed for much longer than normal.

I'm eating normally, stretching as usual, although my legs still feel really tight. Work is unusually quiet at the moment, so I'm a bit bored there which won't be helping. Guts seem to be out too - quite windy! All I want to do when i get home is collapse on the sofa and doze. I'm not sleeping especially well thanks to the stickiness of the current weather (not too bad though), but I should be used to that as work often leaves me with very random sleep patterns.

Any ideas? This is really not my usual behaviour...!

Cheers,

Jon