I've always taken it for granted that your follower/s sleep automatically as soon as you do. Thing is, my UFO (I think it's UFO that does it) gives you the option to make them sleep which got me wondering, does this mean they don't sleep as soon as you do? Do they simply stand around waiting for me to wake up? Another thing that made me wonder is when I hear them yawning shortly after I wake up. So then, do they automatically sleep or have I been missing something all this time?

In my experience, in a vanilla game, followers never sleep or use beds unless you specifically direct them to via the commands. They'll just stand by your bed and watch you sleep all night. Isn't that a charming thought?

Role-Playing will solve all your problems !

Holy! All this time I thought they slept at the same time as me. Does this have any dire affects on them? Trouble is as soon as I get them to sleep and turn off the command function the jerks get right back up again! Which means I can't get one to sleep properly let alone all of them!

Well, sleep deprivation might explain why they keep walking straight into blatantly obvious traps...

Ahem. But no, seriously. Followers do not suffer any ill effects from lack of food, sleep, or water. If it's that damaging to your immersion, the Followers Can Relax mod will let them wander in a set space, and they will often sit, eat, and even run through the cooking animation if there's a cooking pot nearby they can use. They still won't sleep though, since there's no bed assigned to them.

My understanding is, that it is a bug (or sloppy parametrization, to be more exact). Apparently the housecarls' AI is of the type "wander a max distance from your default location", and for some reason, which the responsible developer apparently did not foresee when hastily selecting the type of AI to use, that does not permit them to use stairs. So, if their bed is, say, in the basemant, they will never find it, although it is in fact assigned to them. Lydia's bed is right next to her default location and would be reachable, but it is of the wrong kind(*) and too close to the wall/ceiling, so she can't use it either.

Spouses, on the other hand, have AI of the type "wander freely in this cell", and they can find any object in your house they might wish to use.

Incidentally, the reason why Lydia watches over your sleep in your bedroom is that the chair she sits in is the only useable item she can reach within her given wander range. Even the two chairs in the upstairs hall are just out of her reach. Silly, isn't it? Sometimes she constantly sits down and then stands up, when her AI thinks that it would be time to do something else, but she cant find an alternative.

(*) Edit: Exactly as Lyn1964 describes a couple of posts after this one

How very strange. Spouses but not followers? Even more strange when you see regular NPCs sleeping.

Not strange, really. Merely typical.

(If you are on the PC, Lydia's behavior has been partly fixed in the USKP by extending her wander rage to cover the other upstairs chairs, and marking the bedroom chairs as being owned by the player, and thus off limits to her.)

If you are using UFO, followers will sleep on their own schedule while in "relax" mode provided there is a bed within range that is available to them. At least they do for me. They still won't sleep when actively following unless I tell them to, but as you say they only do so for as long as I keep them in command mode after which they get right back up again.

So if I'm sleeping in a home I own or an inn, I just put followers in "relax" mode until I actually need them again. They go off and do whatever they do, and I can sleep without them standing over me watching. In my player homes housecarl followers will apparently sleep in any bed that's properly coded for the housecarl faction, so while in relax mode I will even see them sleeping there in shifts if there's more than one housecarl currently in residence. Other followers are not so lucky since vanilla homes have no beds that are open to them at all.

In an inn a follower in relax mode will (in my experience) stay in the inn but go off to have a drink or eat or whatever sandbox stuff is available. I just pretend that they've gotten themselves a room (or that I paid for an extra one) and will go sleep in it whenever they're ready to turn in.

Regarding Lydia, while modding Breezehome I found that the bed she gets has only one "activation marker" that is on the far side of the bed and she can only approach it from the near side given the layout of her room. Granted I was tinkering with an existing mod for the house, which made a rather amusing error regarding ownership of the upgraded player's bed it included, but it didn't appear to have touched anything in the housecarl's room so I suspect the bed may be borked in the vanilla files altho I haven't checked to confirm that. If so, then what's keeping her from sleeping in it may not be her AI package as such but the fact that the "approach vector" necessary would require her to go outside the house, levitate up to second floor level, and pass through the exterior wall of her bedroom in order to reach it.

@Lyn1964

Just a minor detail for your information: If you change lydia's bed to be of the right kind (mirror version of the vanilla one), you will still notice, that she can't use it until you move it 60 units further away from the wall.

Well, she may do so in my game, because IIRC the UFO mod 'corrects' a lot of unfortunate follower/housecarl behaviors and limitations.