This video was interesting
http://www.youtube.com/watch?v=T0W4R7QjNfQ
Thanks for using the forum. I am happy to address your questions, and my answer will be based on the information you provided here. Please make sure you recognize that this forum is for educational purposes only, and it does not substitute for a formal office visit with a doctor.
Without the ability to examine and obtain a history, I can not tell you what the exact cause of the symptoms is. However I will try to provide you with some useful information.
In general, hypotonia, or low muscle tone, can also result from problems in the nervous system or muscles.
The causes of hypotonia could include genetic problems, metabolic problems, mitochondrial problems, and toxic problems (exposure to toxins during pregnancy or after birth). Each type of condition can be identified based on a combination of the history, physical examination, and lab testing.
On the surface, your son might fit the description for any of these conditions, but evaluation by an experienced physician will identify some additional features that may not be obvious to you that will help direct the diagnosis. I would recommend that you discuss with your pediatrician if you should have your son evaluated by a pediatric neurologist.
Thank you for this opportunity to answer your questions, I hope you find the information I have provided useful, good luck.