"The reason babies don't sleep through is not because they "don't know how " "
You clearly misunderstood. Babies wake up at certain times in the beginning because they are hungry after a few hours. Then, these waking times persist even when baby gets to a stage when he is physically able to go through the night without a feed, because he now has the habit of feeding at these times. (Just like I have the habit of eating at 8 AM, 12 AM, 3 PM, and 7 PM). Sleep training is done to break this habit, to make the body forget 2 AM and 5 AM (for example) as meal times.
Interesting case in point: In some Muslim countries, during Ramadan, people get up to eat at 2 AM or so, then go back to bed. Then they wake up and fast all day, eating at sunset. Then up at 2 AM to eat again. After a month of this, they still wake up with grumbling tummies at 2 AM because their bodies now think of 2 AM as a meal time. The only way to correct this is to stop eating at 2 AM - ignore the grumbling tummy and go back to sleep. After a few nights, they stop waking up at 2 AM.
"it's for all manner of reasons, teething..."
Not at 4 months, it's not
which is the reason why our paediatrician said it was a good idea to do it before 6 months.
"dreams, itching, illness, indigestion"
And so they don't need to be fed. We went to comfort our babies when they woke up in the night, just didn't give them a feed. And after a few nights, they stopped waking up. Funny how all "dreams, itching, illness, indigestion" stopped so quickly once we started sleep training.
"And you mentioned your medical problems so if they are of no concern to us"
You sound like a lovely person
Well, some of us did care, if you must know.