Yup, been there, done that. And because of it, I always try to spend the first day and night below 7000 ft and spend the first 2-3 days taking it easy, and I haven't had a problem since.
In my case, it was extreme dizziness, almost passed out, couldn't see straight (literally, barely could see), and very hot and sweaty. It hit me after riding the cable car to the top of Sandia Peak just 2 hours after flying in to Albuquerque after coming from sea level (yeah, real smart there

). Rode the car up, hiked to the lookout point, rode the car back down in a very crowded car, got off, and almost passed out. Won't do that again.

In my case, I just had to sit down with a cold wet washcloth on my face for about 20 minutes and I was okay. Weak, but okay. But I was also brought back down below 7000 ft.
DH had some serious problems the first time we took him to the mountains, but we've since discovered that for the most part in *his* case it was car sickness (which he'd never had before) combined with a panic attack at 11,000 feet when he's used to sea level. We now take it easier when he goes to Albuquerque or higher and he's been fine the past two trips, including this trip when he went to 10,000 feet again for the first time in 3-4 years.
The best things I can recommend if you're coming from sea level or thereabouts:
*Spend the first 12-24 hours below 7000 ft, preferably one night so you *know* you're not doing anything. If you're *driving* so the altitude adjustment will be slower, this isn't as necessary.
*For the first day or three, take it easy. Stay in the car for the most part and see what you can see from there, or stay at the cabin or whatever. Don't do any hard hikes, and if you *do* do any walking, take it slow and take deep breaths. Be very conscious about your breathing and that you're getting enough oxygen. And if you feel tired or short of breath, STOP and catch it. Even if you've done nothing but walk 100 feet.
*Try to stay below 8000 or 9000 feet for the first 2-3 days and work yourself up to the elevation if you're planning to do some hiking. For example, first 24 hours stay below 7000 and walk in the parking lot. Next 24, walk around a bit at 7000 but again take it easy.
*Stay hydrated. Especially if you come from a humid environment. It's very, VERY easy to get dehydrated. If you're thirsty, drink water. If you're not thirsty, drink water.

*Know your limits and LISTEN to them. If you start feeling bad, STOP immediately and rest. If resting doesn't help, have someone get you back down below 7000 ft ASAP
*Don't *worry* about it. Be aware of the possibility, be aware of your body and what it's telling you, but don't worry. If you worry and focus on it, you're actually *more* likely to have a problem and panic (another of DH's problems).
*If you do start having a problem, *stay calm*. Do what you have to do to get back to a lower altitude and don't ignore the signs, but don't panic either. If you can get yourself back to 7000 ft or lower quickly (like in a few hours, not a day or two), you should be just fine.
For an example... this trip, when we went up to Pagosa Springs, we spent one night in Albuquerque and even walked slow in the parking lot of the restaurant where we went for dinner. Next morning, did just fine walking at normal speed at
Walmart. Then we went up to Pagosa (just below 8000 ft) and around there even just walking up a slight incline required several stops and left me panting. So, I went *VERY* slow and did okay with it. Two days later, I was able to make that same walk and more at almost normal speed. 6 days after arriving at that elevation, we went to Mesa Verde and I was able to make a 3 mile hike involving climbing up and down stairs and rocks and stuff at about 8000 ft with absolutely no problem, because I'd taken it easy the first few days and worked up to it. Two days after *that* and I was able to walk around on pretty much level pull-overs and take pictures of the mountains on the way to Telluride at 10,000 ft and didn't even realize it was 10,000 ft. No problem. But trying to walk up a hill I had to take it slow again.
The point: Take it easy, and your body will adjust. And if your body doesn't, then get back down to a lower altitude ASAP.
BTW -- where in Colorado are you going?