Feeling hot hot hot! Dizziness brain fog and fatigue!

Vyvanse long acting 50mg and hot weather body response - advice needed! Male 46 y/o. Office work and reduced exercise whilst adjusting to meds over last few weeks:

Just wondering if dehydration is the root cause of dizziness and fatigue. In collee weather it's been a blast and feel side effects.

However it's been getting hotter over last week and have noticed I have no resilience for anything over 20 degrees centigrade. How long it takes to boost electrolytes and all that to rehydrate after days of what may be insufficient hydration? We're in a heatwave to over 30 degrees Celsius here in the UK and it's knocked me over a bit. Been getting progressively more brain foggy and tired in afternoons. Now it's dizziness and is not great at all! I've been staying in the shade and drinking water regularly but doesn't seem to help massively.

I've now started to use electrolytes to supplement plain water and trying to eat more as well.

Just wondering how long it may take to bounce back or it's it's a case of reducing dose or taking a short acting version during heatwaves so my body isn't being so stressed by the heat. I've contacted my doctor for advise as well.

Any tips or experiences will be good to hear! Thanks.