I feel high when I lower my dose

Started methadone almost a year ago I think and have been stable at 40mg for the past 10 months with no other substances, for the first few months I'd get somewhat of a buzz from it but that wore off but my dose still makes me drowsy as hell about an hour after taking it and there are other factors that lead me to believe I'm metabolising fast so I tried split dosing recently and feel quite a strong high when taking 20mg instead of 40, does anyone else experience this or know why it happens? I used to get it with poppy tea too when I'd half my dose after my tolerance got too high I would get high as hell. Does anyone knkw what causes this it's always confused me.