i apologise if that came out as rude, i didn't mean to. i am just a medical student and had the chance to develop a good understanding of how our body works, and i would have been genuinely happy to explain in easier terms, to the best of my abilities, what does drugs do.

I'll keep up the research :)

stimulants do not necessarily increase the levels of norepinephrine, and they most definitely don't on a systemic level. Drugs nowadays can be fine-tuned to work only in specific parts of our body.

if you are interested i would be happy to break down the mechanism of the drugs commonly used to treat adhd.

i believe in ADHD the reduced levels of norepinephrine refer to the role that that neurotransmitter has in the brain connectivity, it doesn't refer to the systemic effects of adrenergic peptides (adrenaline and noradrenaline)

Adrenaline does many things, among which is it mobilises energy sources. This basically means that your muscles get much more access to simple sugar to burn during physical activity. Before, sugar (glucose) was stored away as glycogen, a more compact, way bigger molecule. Imagine this as having to build something with legos in a rush: you have many pieces stored in tall simple towers, but since you are in a hurry you will quickly destroy the towers in order to have a lot of pieces laying around so that you just have to pick them up.

When you destroy the towers (glycogen) that sends a message of fatigue to the brain, both general (you need to rest) and specific for the muscle (you find it harder to move that specific muscle). This happens even if adrenaline is not involved, but adrenaline makes it that most towers in every muscle get destroyed, so you will feel very fatigued. Adrenaline blocked the feeling of fatigue, so you felt it only when it got out of your bloodstream.

This is why you felt "the crash". But why your boyfriend didn't?

Different factors.

• he might have had less adrenaline around, because of past experiences that made him less "scared" of high speeds
• he might have had the same level of adrenaline, but less responsive receptor (i very much doubt this, but i don't feel like excluding it) and that would be completely genetically determined
• he might have had more towers. That depends on how much one eats and is fit, on age and, most importantly, on gender. Assuming your boyfriend is genetically male and you are genetically woman this i the biggest reason in my opinion. Males have, on average, bigger muscles and a more efficient muscle metabolism than females.

It's also possible that females evolutionarily developed a much stronger reaction to adrenaline, because it would make sense to think that when in danger they would have had to also protect children, traditionally in their care. This would justify a much much stronger reaction. But it's just a possibility.

There might be other reasons i am not aware of that could be more decisive in explaining the phenomenon, but this is my understanding of it