Haven't read the replies here, but I will add some bits. 4S can represent a type of restlessness that has to do with people who are highly introverted, who work in fields or in jobs (or in social circles) that require them to be more extroverted than otherwise they personally require. So could be a person who has to engage in constant face-to-face communication and having to forego "breaks" from mainstream society. Can also be someone who never sleeps because of constant chirps, tweets and bleeps that come to them by way of the modern carrier pigeon, aka, cell phones and technology... they want to disconnect from society, even if it's just hiding in the toilet or otherwise being rendered "useless" to the outside world... "I'm too tired, go away"
I'm not really a true introvert, but at work I didn't like to socialize with coworkers because of the very distracting drama of young people, so I would focus on socializing with customers which I thoroughly enjoyed. This is fine during the holidays, but other times of the year it was quite boring. I would help a few customers it felt like, then the rest of the workshift felt largely unstimulating. Come home and had to let that part of my brain "unwind", so I wasn't get the best sleep... so I got this card for the constant state of fighting for rest. My job was boring, I was filling unfilled, so my sleep didn't seem hardly "worth" the effort. In fact, I was regularly sleeping later hours during this time period because I was constantly restless at home.
4S can also be that you are afraid you will never find peace. It's a more sardonic version of a Star Rx I think, in terms of actual "peace"... had to do with more man-made/terrestrial problems, rather than more spiritual loss. i.e. the spirit may be the suffering, but probably more because of man-made issues. For example, people weary of the daily media cycles and political stuff going on in our country... or whose main concerns are not spiritually-related, that is they are in good with God, but because they are high-minded spiritually, they just feel like they are constantly living in-between the trials and tribulations of life... yes this is the "duty" they have to life and society, but it's wearying to be this way constantly and maybe they worry there will never be more to their life than work and sleep.
I think of 4S as the rest between battles, literally. So getting off work at 11pm, only to go back at 8 and slog through. Fearing that eventually you will become so weary in health/mental that you may end up in 4S permanently.... at least until you "revive" yourself. So could be symbolic of a work-a-holics internal mindspace
... they crave sleep constantly, but they don't ever tell anyone, because to say they want to sleep may mean they hate work too... and for some that's all they have.