I have a 17 yr son who wrestles, is in outstanding shape. In the 3rd period, his muscles shut down

I have a 17 yr old son who wrestles. This last weekend at the State Finals, he won 4th at 171 lbs. He is in outstanding shape and conditioning. During his 2.5 hr practice sessions, he doesn´t typically have any issues but at times, his arms do tighten up. However, we had a significant problem this last weekend and wanted to see if you could head us in the right direction. During two of his matches, as he went into the 3rd of three two min. period, his muscles tightened up in that period and he basically shut down. He wasn´t breathing hard, didn´t have cotton mouth, wasn´t sweating excessively, he had pulled approximately 9 lbs by cutting back on eating and drinking a couple of days before. As I talk to him about it, he says he will feel fine but as he is warming up for the match, he sometimes begins to feel drowsy. During the match, it feels basically like after he works out with significant weight to muscle fatigue. Any suggestions on where we should start looking or what tests we should be doing. Any vitamins, etc. that he should be taking. Thank you for your time and information. Chris Sinor Catoosa, OK.