thanks for the replies
it's possible that i did lose quite a lot of salt as i'm a bit overweight and do sweat quite a lot when exercising.
i didn't feel like i drank excessive amounts of water today, but maybe it was too much. i did do a wee a lot more frequently this morning/afternoon than i usually would, so it probably is something to do with salt/amount of fluids. (sorry that's probably a bit too much information
i haven't sorted out what i'm doing yet with carrying drinks with me on a run, so maybe i should be doing that. i was probably overcompensating so i didn't get thirsty whilst running. how much water would you have to drink before you have to start worrying about hyponatremia? is there some kind of formula for knowing how much water/sports drink to take and how often, or is it just a case of practice and knowing your own body?
and how do you guys replace lost salt?
sorry that's a lot of questions. i never thought running could be so complicated - i always used to think it was just putting one foot in front of the other!