Overdose - Future effects after overdose?

[Tryptamine]

Greetings. About a month ago SWIM overdosed on 15mg of roxicodone--which led to headache/nausea vommitting and sick feeling (detailed description here if interested... www.drugs-forum.com/forum/showthread.php?t=88820).

Although 15mg was attempted back then, usually SWIM can feel quite euphoric off of 5-10mg of roxi or oxycodone. But recently SWIM took 10mg roxi after a month from the overdose and hasn't taken any in between. Took 5mg with a small meal, then chewed up 5mg an hour later. SWIM must say, the amount of euphoria he felt this time was greatly diminished, about half of what he used to feel when taking 5-10mg (without tolerance), and he even felt some of the same negative tingling sensations in the back of the head between the spine and the ears on both sides that accompanied the overdose (though not as extreme and without nausea this time).

The question: Could the overdose have effected SWIM's ability to feel the euphoric effects from future injestions of roxi/oxy (because of brain/receptor damage, etc.)? If not, what is most likely the cause of this diminished effect (e.g. could tolerance exist after a month, that it was taken with food)?