Various prefixed verbs, such as recumbō "lie back" and succumbō "collapse", seem to point at a basic form *cumbō (-ere), meaning something like "lie down".
However, as far as I can tell, there is no such verb. Instead, we have cubō (-āre) with that same meaning, and a handful of derivations from this, such as accubō "lie at" and incubō "settle onto (v); nightmare (n)".
These two verbs certainly look similar, and my first instinct is that cumbō is just cubō with a Proto-Indo-European nasal infix (cmw mentions Greek λαμβάνω vs λάβον). But I haven't been able to find good etymological information online.
What is the origin of these two similar words? Do we know what happened to unprefixed cumbō that didn't happen to its prefixed forms?