[QUOTE=secondteam;8000906]
Definitely talk to a doctor about it! I had a similar issue that turned out to be something called postural orthostatic tachycardia (basically, low blood pressure/high heart rate causes lightheadedness and I occasionally pass out when I go from sitting to standing, or change position - like when dismounting). Staying on top of hydration and eating more salt helped a LOT but I never would have figured out what was going on had I not seen a cardiologist. Now I very rarely have these issues unless I’ve been doing some serious cardio.
In the meantime, definitely keep up on your water intake. My biggest tip is to get one of those big plastic 32-oz water bottles and bring it to the barn with you, especially if you only get these symptoms when riding. Drink the whole thing over the course of your time there (some while you’re tacking up, some while you’re cooling out, etc), and don’t forget to take breaks to drink during your ride! Taking those five minutes in the middle of your lesson to rehydrate is so important, even if it’s freezing cold.[/QUOTE]
This! I have this as well, and was ‘diagnosed’ by the Holter monitor test eclipse mentioned.
Its technically not a diagnosis, because many things can cause it, but an umbrella term for the symptoms including syncope, over heating, tachycardia, fainting, nausea, etc. that are sometimes hard to pinpoint what exactly is causing them.
Eating salty snacks and making sure you are drinking lots and lots of water will help a lot. When starting or stopping activity, or going from standing to sitting and vice versa, be sure to perform these actions slowly. Maybe, for example, go from a canter, to a posting trot, to a sitting trot, and then walk? To keep your heart rate and blood pressure from slowing to suddenly. Doing things like picking out feet and dismounting are often times I feel it.
As others have said, however, be sure to go to the doctor! They can accurately tell you whats going on and make sure nothing more serious is afoot 