They're sometimes called " middle verbs " ( no Wikipedia article as far as I can tell ).
2.
It is also probable that some Early PIE middle verbs also became thematic in the Western PIE period, since they lack middle correspondences in Anatolian.
3.
There is also a valency-decreasing verb-prefix " ai-" which, added to transitive stems, produces unergative, reflexive, reciprocal or middle verbs.