noun, na-adjective, noun which may take the genitive case particle 'no'
hyperconsciousness; excessive self-consciousness; overthinking
Refers to being overly aware of oneself or a situation, often imagining things that aren't there. Commonly used in the phrase 意識過剰になる (to become overly self-conscious).
He is overly self-conscious about his appearance.
I become hyperconscious even of a casual glance.
自意識過剰 specifically means excessive self-consciousness, while 意識過剰 can also refer to being overly aware of external things or situations.
Compound of 意識 (consciousness) and 過剰 (excess). The exact historical derivation is uncertain, but the meaning is transparent from its components.