I use the camel method all the time when backpacking and haven't had any issues. I'll genarally down a liter of water while I'm filtering then sip while I hike the rest of the day. I've really only heard of Hyponatremia in marathoners or triathletes and the odd college frat hazing rituals. Hikers generally stop and eat lunch and snacks while hiking. Most of the people affected with it have been drinking gallons of water in a short time on a dare, or are in long duration events where they are sweating water out as fast as they drink it and unable to snack or drink sports drinks readily.