Yeah, none of those. I don’t think it’s actual “classical” music.
There's this drunk in a bar and it's just him and the bartender.
The drunk wants another drink but is out of money.
The drunk offers to sell the rights to some music he wrote for the price of another drink.
The bartender isn't going to be cheated so he tells the drunk to play it on the piano and if he likes it he gets his drink.
Drunk proceeds to play this fantastic tune that the bartender had never heard.
Bartender pours him a drink... and asks, why haven't you sold this to a music publisher... Drunk says he's tried but the music keeps being rejected.
Bartender asks: What is the name of the song? Drunk answers, it's "I love you so F'ing much I can't Sh_t."
Do you remember whether it was performed on acoustic/conventional instruments or if it made use of electronically generated sounds? Was there a vocal component?
I can’t help but think of theme music from Doctor Who or Outer Limits (or even Twilight Zone, but surely you’d not be asking if that were it). There must be a dozen TV shows either from PBS (maybe even Carl Sagan’s Cosmos?) or Sci-Fi serials from the 60s-80s which had themes that could fit this description.
If it possibly may have been classical, then Danse Macabre might be another candidate because of its intrinsic creepiness and slightly comical quality—although I can’t imagine it being associated with lethargy.
I know you already said no to someone else who mentioned the Blue Danube. It’s the first thing that came to my mind as well, which is a perfect match for lethargy and dreaminess thanks in part to it’s use in 2001: A Space Odyssey.
Oh, I also have a vague, nebulous recollection that there might a clip of instrumental music vaguely fitting your description that was played along with Pigs in Space sketches on several episodes of the Muppet Show?
Of course there are some smart phone apps and websites that have a tool for you to use a microphone and basically hum the melody so that their system can search for matches. I’ve heard that such programs are surprisingly sophisticated and capable.
Do you have a rough estimate of what time period the music originated from?
There are some musicians that used to be categorized as New Age or Eclectic that I think produced a lot of tracks roughly fitting your description. You might consider Andreas Vollenweider or Vangelis (Famous for Chariots of Fire, but also did some “quasar” sounding stuff particularly on their Albedo .39(?) alblum) or maybe the Mannheim Steamroller or Mark Isham or Shadowfax or Wendy Carlos and the Moog (famous for A Clockwork Orange soundtrack and some of the Original Tron soundtrack).
Of course there’s also Daft Punk, who recorded the soundtrack for the 2011 Tron film.
Maybe something here will send you down a path that will jog a memory that will get you a bit closer.