What you describe sound exactly like a classic fit, though could be many things, this can show from a momentory absence to a full blown thrashing fit. The circumstances ie only in the summer suggest a trigger that may be related to fitness, heat or just excitment. If it is fitting find the trigger and avoid.
Alternatives are cramping that can present as a stagger/loss of control, strange gait etc, again avoid ie don't run in the heat. Be careful of electrolyte suppliments unless you know for sure that there is a shortage of a mineral salt as adding the wrong one will only make things worse.