Summer brings out the worst in people; some days it feels as if the temperature rises one more degree. A seasonal raise in violent crime may be due to discomfort and irritability, but can the weather actually drive you crazy?
It depends on how hot it is, and whether you're mentally stable to begin with. Intense heat increases the risk of dehydration, and even mild dehydration can affect the brain. As per experiment and study done with two dozen college-age men has found that a loss of 1 percent body mass via exercise-induced sweating (replaceable with three glasses of water) decreased their cognitive performance and increased levels of anxiety.
Dramatic overheating can also lead to heatstroke, symptoms of which progress from confusion and irritability to hallucinations, violent behavior. In animal models, overheating causes some neurons to become more excitable, which might underlie the psychiatric effects. Most of these are transient—cool off and they go away—but heatstroke may lead to long-term brain damage. (It can also kill you.) You won't keep hallucinating for years to come, but you might end up a little clumsy or slur your speech. Case reports of long-lasting personality changes (similar to those caused by traumatic brain injury) also exist, but this complication appears to be rare.
Easing into the muggy weather makes heatstroke less likely, this may be why sudden hot snaps have been specifically linked to increased suicide rates. In South Australia, it has been found that hospital admissions for mental disorders increased at temperatures of 80 degrees or above, with schizophrenics being at especially high risk.