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I'm happy that you have asked me to assist you with your grandchild and hope that you can benefit from my many years of helping grandparents like you.
No, I don't think that there is anything acute or dangerous going on as long as he seems otherwise fine, alert, talking well, balance OK, etc.
He needs to see his doctor though and then perhaps a neurologist as it sounds like he may be having some type of seizure, which would not be unusual in a child who had a stroke and the resultant scar tissue in his brain, even this late.
The other thing to consider would be his heart and perhaps having some type of arrhythmia but his doctor can check this out as well with an EKG.
I see you are offline but if you have any further questions please let me know as I'll be online the rest of the evening and want to be sure I address all of your concerns.