Low tone clarification question.
To piggyback on the question below without totally hijacking the thread . . . .
Why is low tone always a symptom of something?
And when you say low tone affects all muscles, does that mean that all muscles should be equally lax?
We struggle with this concept. My husband is an "apple" shape, as are his dad and grandfather. My family have severely large heads. Our son has struggled with head control, head lag, and low tone in his trunk, and his head size is in the 90th percentile. He also wears a one-pound helmet for cranial molding. We have other parents tell us all the time that their kids struggled, too, but after a late start developed typically.
But, since our son has epilepsy, we have been on an unending roller-coaster from specialist to specialist to therapist, half of whom insist there is some underlying issue just waiting to be discovered. They say this is because of the combo of epilepsy and low tone.
I guess I am just trying to wrap my mind around this whole low tone concept. It's hard to mentally prepare yourself when friends and relatives are all telling you your kid seems fine but then you spend what feels like half your life in a health care setting with people who use mysterious terminology and are always sending you on a wild goose chase for second opinions and specialist and expensive therapies.
Thanks for reading this long rant. These months of questioning, wondering what his future will look like, and not feeling like anyone really understands have taken a toll on my mental health. Any better understanding of low tone you can provide will be greatly appreciated. 
Re: Low tone clarification question.
muscle tone is controlled by the brain. It helps us be ready to move. There is a wide variety even in people without any diagnosis. Some people just have lower tone than average for whatever reason. It usually takes longer than average for them to reach milestones because they have to generate that much more force in their mucles to move. The extreme in either direction usually does indicate a problem in the brain. High tone makes it hard to move in a controlled way because the muscles are always "on" if that makes sense. On a personal note my kiddo has a seizure disorder. He has probably low average tone. I think his medicine is impacting his some as it is slowing his brain down to prevent seizures. All his tests are normal and his brain has been cleared from what the specialists know anyway...
Low tone is not always in all the muscles equally.
In his first month or so, DS had low tone(hypotonic) in his trunk and high tone (hypertonic) in his legs and arms. His arms and legs have evened out and now we are still dealing with low tone in his trunk. He has neurologic stuff going on in his brian due to chromosome deletions.
The nerves sending impulses to the muscles all are controled by the central processing system in the brain. If something is up with the "main computer" more than likely it will show up on musculature system. I wouldn't say it means there is something "wrong", rather something "different" is going on.
sounds just like my son....low tone, lack of head control, helmet, seizure disorder. i think he is slowly getting better but not there yet. and he has so much better head control when you hold him than when he's on tummy time. did a slew of genetic tests, so far nothing.
My guy has lower tone on his left side (hand and forearm). He started out with focal seizures (left leg) at about 24 hours after birth, and was diagnosed with a mild stroke (ISA, MCA, right side) about 48 hours after birth. We're struggling with it a little, but OT is really helping.
I agree with PP in regards to being assertive. It's almost like sometimes the healthcare professionals that I deal with forget that I'm a real (normal, as in non-healthcare) person.
I've posted this before, but I'll say it again. Having a notebook to write everything down in, at every appointment has helped me. It also gives me stalling time to process....I too am going bonkers from spending so much time in hospital-ish settings. Hope it all gets better for you soon