Hi Doc. My Son Aged 10, Was With Me For

Hi Doc.
My son aged 10, was with me for hair cut ,and was enjoying and talking and was chatting around suddenly asked for water and winth in time span of 3-4 min his lips turned white and lied down and wanted to sleep .. not even willing to talk... I rushed and gave him water with full adult dose of elcetrolit in glass of water.. he sipped one glass and in span of 5 min .. he was perfect and playing.

this is 2nd incedence in last 3 months.
please suggest.