Good to hear that your teen age son is not having numbness or pain.From the history you narrated I should warn you that your son is having a mild TIA(Transient Ischemic Attack
) i.e, having said that he had flutter , there is a chance of an embolism
which travel from heart to the brain and can occlude small arterioles in the brain and lead to slurring of speech.
My personal opinion is that he need further tests like CT/ MR angiography
to see whether any ischemia
or embolism has occurred in the brain.And an echo to see for vegetating in hearts valves.
If not then its well and good but you have not mentioned whether he is on any drugs like warfarin
if so then need to do blood tests to see INR .
Wish you a Happy New year