... I get severe headaches if I don't drink enough water or if I go for a long walk/run. Is this normal? I was on it for a year then tried to take myself off it for about 3 months and have started on it again (for the better). I'm taking 900mg a day. Any answers or advice would help. Obviously I'm trying to drink about 2 litres a day and more after exercise but I didn't know long walks/runs would also affect my lithium levels.