Want to point out that (while I have no experience with LSM yet) sedation with lysergamides is not unheard of, just look at LSA-containing seeds. Lethargic woozy high dreams... is that not a possible description for both LSA's as well as morphine?
Considering there are no lysergamides with micromolar affinity for opioid receptors - that I know of - it is pretty unlikely that modifying a diethyl amide into the morpholide would suddenly lend it that property. I would need to see some seriously compelling evidence to suspect that.
Not really sure what lethargic dreamy trips from pharmacologically different drugs share in action, if necessarily anything. The 'how you feel is a poor way to actually tell' sentiment is a good one, one that I would echo. Nevertheless, I am interested to hear if the sedated feeling is anything like that of LSA-seeds.
@LSP being more likely: it would not be UK legal, would it? I think "Lysergide and other N-alkyl derivatives of lysergamide" is in the misuse of drugs act, and LSP would be covered.
edit: Additionally: reports of unusually unreliable potency and instability in solution (degradation into inactive iso-LSD) which logically accounts for said unreliability?? That makes me suggest that you be extra stingy with how you treat this substance. Use desiccants, invariably... avoid making an aqueous solution unless you plan to consume it quickly or evaporate it onto some kind of carrier (in which case don't make your solution so aqueous).