PO is Latin for "by mouth" so it is referring to taking medication orally. APAP is an acronym for acetaminophen which is generic Tylenol. Percocet is oxycodone and acetaminophen mixed together. The amount of each is listed on the bottle as */*mg (e.g. 5/325mg which would equal 5mg of oxycodone and 325mg of acetaminophen). CWE (cold water extraction) is used to decrease the overall amount of acetaminophen to prevent liver damage. The maximum recommended amount of acetaminophen in 24hrs is 3000mg. So depending on the strength of your pills and how many you are taking (I'm assuming it's a fairly low amount) you may not need to worry about extracting the acetaminophen at this point. It is also best used for large amounts of pills at once as the fewer the pills you attempt to extract the more active ingredient you lose in the process. CWE is necessary for higher doses if you begin taking more though to prevent complications. If you start taking more ask your doctor for oxycodone without the Tylenol. You can say it upsets your stomach or that you're worried about the long term effects of high dose acetaminophen on your liver. With you being a cancer patient I don't see why they wouldn't change it for you.
As far as strict amounts to stay under to prevent overdose, this largely depends on your current tolerance (how much oxycodone you are using regularly for pain) and your natural tolerance to opiates (everyone is different, what might be too much for some would not be enough for others). If you are only used to 5mg percocet doses I would not exceed 15mg your first time. If you choose to increase your dose during subsequent sessions I would increase by 5mg increments until you reach the dose that works for you.
And lastly, I'm sorry about your son. I have two sons myself and could not imagine how it would feel to lose them. Drugs are a small bandaid over a gaping wound when dealing with severe grief. Are you seeing a counselor? If not consider it. I understand you are just looking for some relief from the pain (both physical from your cancer treatment and emotional from your loss) but in the long run numbing yourself with opiates will cause you even more pain. They will also become less helpful at treating your physical pain if you begin to abuse them. Once your tolerance builds you will have a difficult time getting relief from reasonable dosages when you actually need them.
Be cautious and reach out to someone you trust to talk about your situation. There's a great group of supportive people in the forums here on BL. Check out the Dark Side.
And keep asking questions before experimenting to keep yourself safe. Welcome.
