At least you know it’s all normal. It’s surprising how a simple drive out and back again takes so much out of you due to the over stimulation of the brain. He does have to subject himself to this stimulation in order to become used to it again. But it will take a lot out of him. He has to expose his senses to different levels of sound, visual stimulations, even scents such as: traffic noise, cars moving in all directions, people too, music, talking, shouting and crying, people moving in all directions, the scents of traffic fumes, perfumes, foods, different levels of lighting such as the daylight, traffic lights, blinking lights of cars - the constant change of them all.
It all has to be taken in and processed by a brain that is currently running at a reduced service. It has to do all this whilst at the same time mopping up, repair and relearn. It’s ability to multitask is strained 
And when it all gets too much the best you can do is sit quietly for a while or take a nap 
It can and does get better over time, it’s that in meantime you expose him as gradually as you can, in small doses. There are times that’s never going to be possible and for those days, you just try to aim for a quiet day for the following day or two. It’s all about good management of fatigue and the first thing being to recognise and accepted that this is a thing.
One of the disadvantages of managing fatigue is you get so used to the routine that you forget fatigue is even an issue. Until a day comes that you do something different and you’ve not prepared yourself for it; as I explained in the post below 
Lorraine