Increased respiratory rate, increased heart rate, increased BP. This low O2 sat of 65% will not sustain life. You may lose eye sight, short term memory, and your strength and stamina, progressive weakening of your heart muscle will contribute to heart failure. A person may get so weak they just want to go to "sleep".
Not a medical professional, but the long term consequences of hypoxia (low O2 sat) include an enlarged heart. That damage begins in the low 80%'s. It is really not something to mess around with. Whoever you are talking about needs good medical care an to be on O2.
Take care.