I've had headaches for as long as I can remember. Sometimes I get them two or three times a week, sometimes I can go for a week or two without getting one. Most of them are pretty tame... kind of like a low-grade hangover. It always leads to, or derives from tension in my upper trapezius muscles. Consequently, or perhaps even because of it, I have terrible posture. Having an IT job just magnifies that.
Last year I started doing Pilates a few times a week, just following a video. I initially started doing it so I could "increase my core strength" in the hopes that doing so would help/make me sit up straight and lead to less headaches. While I was doing it, I found I got less headaches. I liked doing it too, so I'm not sure why I stopped. It's one of those things that I say I'm going to do again tonight, but never do.
I also started running last summer, following the Couch to 5k running program. I made it as far as week three before getting hit by a car on my Vespa and being off my feet for about six weeks. Around September I got back into it and worked my way through all nine weeks and even during a week-long business trip. Right before Christmas, I hit my goal of running 3.1 miles or 5k without stopping.
I spent a lot of time in airplanes so far this year and my running regimen suffered for it. So much so that when I started back up again in February, I stepped back to week five and struggled to get beyond two miles non-stop
At some point in March, I woke up one morning with a stiff neck. No biggie, I slept on it wrong, took an Advil and carried on. Three days later it still hurt and was affecting how far I could turn my neck. I went running a few more times but found that when I did, I got a wicked headache afterwards.
After nearly a month of constant pain and a constant stream of Advil, I broke down and made an appointment with a chiropractor. I'd never been to one before, and was always "warned off" by my mother about them, but whatever, I was in pain and it might help. (That it was also covered by my health insurance was a bonus). I showed up the first morning at Dr Khan's office (he's from Kelowna of all places!) not sure what to expect. We talked about what was going on and he gave my spine a pretty thorough going-over. He noticed immediately my poor posture. The exchange went something like this:
Dr: "You carry your head very far forward, so you've upset the natural curve of the upper spine."
Me: "OK"
Dr: "This then puts a load on all the muscles in your upper back, neck and shoulders.. they get tired out and then they knot up, and that causes headaches"
Me: "OK"
Dr: "How long have you been getting headaches?"
Me: "I don't know, really... I can remember as early as grade four or five, so... 25 years?"

Then he started prodding up around the top of my neck, said "oh..." and then "tell me if you feel this..." and then pressed on the knot right up at the top there and I heard a choir of angels singing the Hallelujah Chorus and everything turned white. HOLY SHIT ON A DOG that was an intense, searing bright pain.
Dr: "I think we just found a trigger point"
Me: (breathing a bit heavily) "Ya think??"
After that he had me lay down on the bench and started cracking. The first couple crunches were so loud and such a shock that my leg kicked out a little! After that he moved down and did some cracking on my upper back, down between my shoulder blades and then had me roll over onto my back and get some other pops and cracks out of my neck again.
I was almost in a bit of shock over the noises and crunchiness of my spine, but by the time I stood up... my head felt lighter. I could turn my head to the left almost as much as I could a few weeks before... and my whole back felt... good! I was having a hard time not grinning like an idiot and I remember thinking to myself WHY the FUCK did I wait so long???
Over the next few weeks, I went in three times a week and during that time we were able to restore full mobility to my neck, and he showed me what my posture looks like now, and what it SHOULD be. Wow. Very cro-magnon.

I've made a follow-up appointment for later on this month, but I've still been getting some headaches in the last week since the last appointment, so I may end up going back sooner than that. At this point, every visit is just a $9 co-pay so I'm not too worried about that.
After consulting with the Doc, I asked him if he had ever heard of a nadachair. He hadn't so I printed it out and brought it into him the next appointment. I saw it reviewed on Cool Tools about a year ago and kept it in the back of my head. It's a strap that goes around your back and then has some webbing straps that go around each of your knees. You cinch the straps down and it forces you to sit up straight.
I ordered one that afternoon and had it sent to my office in Miami and then someone brought it down for me a few days later. It does work as advertised. I've actually got it strapped in right now and I'm sitting up straight at my desk. I find that when I release the buckle and stand up out of it, that my muscles in my lower back are a bit sore because, you know, I don't use them normally! When I sit back down again without it on and can feel myself start to auto-slouch, I can totally feel the difference and sit up straighter. I've yet to try it on an airplane, but with my schedule, I'm sure that won't be too long :)