Your Biggest Workout
If you can take the emotions, cheering fans and adrenaline rush of crossing the finish out of your mind for a second, your marathon experience boils down to one thing: your longest--and potentially hardest--run all year and perhaps in your life.
Just as you took care of your body after those critical 16, 18 and 20+ mile long runs on your way to race day, so too must you care for your body now. Given the demands of the race, and how much of it you truly "raced," you have placed a massive dose of training on your body. If you can recover properly, you can not only avoid burnout or injury, you could set the stage for an even better training cycle in the future.
The Weight Room
Since most of us have lifted weights at some point in time, I think it's helpful to draw a parallel between your marathon and the weight room. We've all gone to the gym after some time off, piled the weights on the bar and had a good session...only to wake up the next morning practically paralyzed.
Your muscles do significant work, and they need to recover. It's the recovery, not the lifting, that makes you stronger. After all if you go back on the bench that next day, you'd probably drop the bar on your neck! Savvy weightlifters alternate body parts, making sure that they are well-recovered before attempting another session.
This powerful experience is not that different from what your body undergoes during a marathon. There is deep muscular fatigue from the effort, not to mention the cost of actually covering 26.2 miles on your feet and legs. If you can understand this physical state to be an opportunity, instead of an inconvenience, you might well be able to absorb the work done and earn some significant fitness.
Phase One: The First Hour
Once you've crossed the finish line and have your medal in hand, it's imperative that you turn your focus towards recovery. You can start doing the mile splits and swapping stories as soon as you have taken a few basic steps.
1. Dry Clothes -- Once you stop working, your body will almost immediately begin to enter recovery mode. Even on a warm day you'll find yourself getting quite cold and clammy; avoid these post race chills by quickly changing into some nice warm soft clothes. This includes footwear, and injuries aside, another pair of shoes is best (as opposed to sandals) so as to keep your feet from swelling up and to provide you with much-needed support.
2. Feet Up -- After your quick change, you'll want to find a way to lay down and get your feet up. After several hours of hard work, your body needs help facilitating blood flow. Besides, this is just plain relaxing. Make sure you are well enough to be alone or have a spotter keep an eye on you, and just lay down. Ideally you'll be able to keep your feet up for 15- to 25 minutes at this first go, and it's recommended you do this several more times during the day.
3. Quick Calories -- You'll need some kind of recovery meal, ideally in liquid form and containing some protein. Avoid processed fruit juices or other sugary substitutes; use what has worked in training but make sure this happens in the first 30 minutes after your event.
4. Care for Damage -- If you have sustained some kind of injury such as a blister or muscle strain, now you can begin assessing the true extent of what you have done and seek out help. Your brain will be much clearer, and if you need to go somewhere or wait in line at least your basic needs will have been met.