meaning of near the absolute limit

[Learning_English]

"Very much pain" means a large quantity of pain but says nothing about the degree. It could be pain, mild or severe, that covers a large area or pain that goes on for a long time or pain that recurs often.

"Severe pain" is serious in degree. It could be localized and not last long, but it is serious enough to warrant a trip to the emergency room to find the cause because it could be something disabling or even deadly.

"Extreme pain" is near the absolute limit of tolerance before losing consciousness. Not all severe pain is extreme, but extreme pain is very severe

Could anyone explain the parts in bold?
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Please let me know if I have made any mistakes in any of my sentences.

[Mister Micawber]

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Near the absolute limit of tolerance = almost as much as one could possibly stand/endure.
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Native English teacher at Mister Micawber's