Point of order: if you can come back after a few weeks of rest you’ve “overreached” not overtrained. Overreaching is basically a less serious, more temporary version of overtraining. If it takes longer than a few weeks to recover, you’re overtrained.
Unlike others here, I would recommend backing of entirely. A few years ago I trained myself into the ground and by the time I realised what I’d done, I really couldn’t even get through easy workouts. However, I had races planned and would force myself out there prematurely. I had shit-house workouts that did nothing for my fitness and only served to prolong my recovery. For me, recovery took 2-3 months.
Personally, take two weeks off completely. No easy training. Nothing, zip, nada, save for maybe a trip to the pool where you focus on form. Listen to your body and monitor your heartbeat first thing in the morning. If your heartbeat is elevated just after waking up, it’s a good sign you need to take it easy. Monitor your mood: there’s good correlation between depression / anxiety and overtraining. Only return when you feel like that lingering fatigue is gone and you actually want to get back into training, not the usual “I have to train because my competition is out there getting stronger” type motivation. Pushing it early is only going bury you further into that hole.
While you are sitting around recovering, read this (long) series on overtraining and overreaching. It starts here: http://www.bodyrecomposition.com/training/overtraining-overreaching-and-all-the-rest-part-1.html (no, I’m not a shill for Body Recomposition, but there is some seriously good info on that website). Read the whole thing. It’s long, yes, but informative and (towards the end) eminently practical.
Here’s the money quote:
What to Do if You Overtrain
Rest.
Seriously, that’s it, that’s the exciting conclusion to this series. If you’ve screwed up and trained too hard for too long with inadequate recovery and dug yourself in, the solution is rest and recovery for as long as needed to get out of the hole. It might be weeks, or months or longer depending on how deep a hole you dug. But you must rest.
And nobody can say up front how long it will take. It doesn’t really matter. You rest and recover until you’re rested and recovered. You can’t force the process and all you can do is be patient and let it happen. But now you wonder, what should you be doing during that rest period.
It’s would be ideal to start with 5-7 days completely off from training. Brisk walking tops during that time period and nothing more intense. Just go rest and sleep and eat and recover. Get some massage if you can afford it, at least foam roll. Epsom salt baths, relaxation, the stretching you’ve been skipping the last months. Watch your nutrition. Whatever you need to start the recovery process, now is the time to kick-start it and a full 5-7 days totally off will do that.
Good luck.