I notice that my housecarl follower is no longer ... following. It is possible that the person got into my way in a doorway someplace and I may have accidently hit (Stay here). However, that was a couple of hours ago as I was roaming around the continent doing little homeburglaries and whatnot. I cannot possibly remember exactly the last time I saw the housecarl. Is there a way to reset and have that person show up at my side? Simply exiting an area doesn't bring that person to me.

Well ... discovered one way. Sleeping in one's own house brought the housecarl home. Had to speak to the person and instruct them to follow again. All is well.

If you don't own the house yet, you might want to check the hold (i.e. Dragonsreach) where you got the housecarl. You'll find her sitting at one of the tables.

I had this situation with lydia it took quite some time for her to return (from solitude to white run) i fast travelled home after I had the message about a follower not waiting, and she was not there, i checked home and dragonreach, I thought I'd lost her for good so went to another 3 or 4 cities including coming back to whiterun and on the third visit back she finally arrived.

Lydia (and I suspect any Follower) always makes her way back to you unless you tell her to stay somewhere.

I suspect she teleports, but it`s smartly done because you never see her teleport, thereby keeping the suspension of disbelief that she somehow found her way to you by foot.

Good.

Which was what I believe happened. The "stay here" command caused me grief as I attempted in vain to retrace my steps in search. The housecarl simply wasn't showing up anywhere. Only actually sleeping in my own housebed did the trick. Dunno if they would have shown up at the table of the jarl ... wish I woulda looked there.

As i understand, eventually the follower will depart if you tell them to stay here, so should always return, I have not seen anything to contradict this, done with 3 followers at various times (one being a special daedric quest follower who is rather annoying)

After about 3 days, the follower will discontinue the "stay here" order, and return to where they normally roam.
Depending on if your housecarl usually resides in your home normally, (since you can get one in the main quest without having a home), they will show up back at your house in around 3 in game days.

If your follower does not reside in your home, they will go to where they usually reside. So, in the case of Lydia, she'll go back to Dragonsreach if you don't have a home for her to guard.

If you play Skyrim on a pc, you could do "player.moveto ID" ingame without the quotation marks to teleport you to whoever the actor's ID is.
As for the ID of your housecarl, you can check Skyrim wiki or uesp.net

Oh, I did this once. Once. I told Lydia, laden with dragon bones and dragon scales I was going to use to make a suit of armor to stay put while I sneaked into this place (she kept tripping the floor plates) and I took the shortcut out fast traveled back to town, did a quick quest, and then went "where is Lydia?" Then "Oh, crap. I told her to wait, but where?" Then I searched three caves for her and found her in the next to last one I'd been in about mid-way through it. She should have had a smart-assed remark to make, "About time you got back. I was running out of Draugr to eat."