An exciting drive with my wife

But it makes the driver feel sleepy. I can say this with personal experience.

Yes. Personally I find it a violation of the road code. The driver must drive- so it’s the copilots job to assist in navigation, spotting police vehicles, hazards, or points of interest the driver may miss. They are also the designated assistant to the driver in furnishing food, opening packages, operating electronics, and searching information like when a place closes or whatnot costs etc. that is relevant to the plans. The driver can’t sleep and just wake up there or hours closer- so the copilot is responsible to keep them awake and entertained as well with conversation and jokes or games. Back seat passengers may sleep as they wish since cross seat communication is difficult and they lack the access to provide assistance or spotting that the co pilot has.

One exception to this rule is of course where a pilot and co pilot will be switching places for a very long trip so that driving can continue without the need to stop. Then it is acceptable that the co pilot sleep so as to be rested for their shift at the wheel. Those incapable of properly performing co pilot duties or with medical or other conditions- or extenuating circumstances of lack of energy etc. are also excused, but should sit in the back seat if there is another passenger able to take the copilot duties. There are also other exceptions based on personality. Some drivers may hate “banter” or may get irritable when tired, and of the copilot also does- having two irritated people stuck in a car without sleep is bad, and can be worse when you arrive at your stop. Having one rested person who can let the others crankiness “slide” can avoid issues.