What's with these 2 distinct "stages" with Vyvanse

So for context I started off with 10mg in July then slowly increased until my current dose at 40mg (slow acting - I think) which I've been taking for about a month now. I've had barely any breaks because without my meds work and uni feels like a cosmic-horror from the pits of hell and I don't enjoy that very much. My "honeymoon" phase has ended and so I don't physically feel the meds kicking in, but I do notice from my mood, mindset, side effects (dry mouth and lack of appetite mainly. I don't really mind either) and, obviously, focus! Unfortunately it does nothing for the procrastination which is a big issue for me but oh well.

These past couple days, I've noticed that my meds seem to be coming in two distinct "stages" when it comes to my mood. The first stage (about 2 hours aka when it "kicks in" to 4 hours) makes me super optimistic and bubbly and happy (which is how my personality naturally is but I've def noticed an increase). I have way less anxiety, less irritable, etc - so I think that's why. At work I'd go from "I hate this and everyone" to "yk what actually this is pretty ok". After about the 4-5 hour mark, I suddenly get super super calm, kinda sleepy, sorta apathetic, zoned out except for the thing I'm (now completely) focusing on, mind blank no thoughts head empty; almost "like a zombie". This did happen the first day I started 20mg but it hasn't really happened since. The focus is all still there though! It's moreso my emotional state. I've also been eating more protein lately if that's been affecting it...? It doesn't really bother me that much but it has been making work harder because I start becoming annoyed by customers again (like "I'm not up for small talk don't remind me that I exist just let me zone out and ring up your items").

My meds don't work at all the week before my period for some reason (or at least they're veryyy dull). I've noticed that they haven't really been working these past 2 days which makes me think my period might come 2 days early? So I can't really keep testing to see how long this 2-stage feeling will consistently last for until 5 more days go by.

Does anyone also have experience with this? Is there a reason why it seems to only be acting like this now even though I've been on 40mg for like a month now? Before it was more like a consistent blend of both rather than these two very distinct stages. Works in my favor for uni lectures at least...?