I constantly flip my schedule from graves to days. I have a hell of a time adjusting, but it can be done. To stay up for 27 hours is nothing, as it is easily achievable. I guess I am used to working and staying up for sometimes 48 hours on occasion.
At about 7:00AM, I down a red bull. I drink a small cup of coffee every 2 hours, or sooner if needed. I put alot of sugar in the coffee, as it gives me the crack addict feeling (LOL! Never did crack by the way!). Continue to drink coffee until about 3:00PM. Then have yourself another Red Bull. While this is not healthy, it works to keep me going until about 7:00PM. If you sit down, you will start to feel tired. Get up and take a walk. Seriously, it works. It really helps to be outside and in the sun. Be sure to eat good, as the coffee and Red Bull can take its toll on your stomach, and give you a heck of a headache.
When I flip my schedule, I normally get a headache for the first 2 mornings of waking up. Excederin Migraine seems to be the best, but sometimes I need about 600MG of Ibuprofen. I am sure it is caffeine withdrawls, or just the body timeclock saying "WHAT THE HELL ARE YOU DOING TO
Good luck and keep us updated on your marathon! LOL!