Fiction Writing Marathon - Pros and Cons

I spent the weekend at my friend's house (who's also my co-author on the Epic Collab Story I mentioned over and over again). During that time we wrote non-stop for hour, and the story is now over 22K (and it's not even half of it).

You could say that those three days were some kind of a Writing Retreat. Since apart from writing our story we also spend most evenings (and nights) brainstorming ideas for our next collaboration.

Yes, those brainstorming sessions weren't always productive, as too many of them included a variation of the "I'm Batman!" joke. But in the end we did come up with a very good idea that will most likely consist of two longer stories.

I'm sure it's not a secret that after an incredibly productive couple of days, every writer feels satisfied and accomplished. I did too.

But there's a problem with spending so many hours writing. For a few hours after returning home, I felt burnt out. It was as if no words that left my brain and appeared on my screen were good enough. I felt exhausted and I just wanted to sleep (and eat). Not to mention the fact that no posts and articles I wrote in between the writing sessions felt like they were up to my usual standards.

So, on one hand (huge Pro), I wrote an obscene amount of words during those two days. I moved the story along and followed the outline, including some really fun foreshadowing.

On the other hand (a huge con), it really feels like too much in too short period of time. My brain is used to creativity being spread over several days, due to my schedule and fitting the writing after my day-job.

I know I can do writing marathons, I did that in the past when I had a deadline to meet and I wrote over 5K in one day. But this weekend showed me I can't do such an intensive writing all the time. Maybe I could do it once every few months. Maybe even once a month.

Have you participated in Fiction Writing Marathons before? Do you have a routine for insane days when you just write and write and write? Any tips for when I do the writing marathon again?