This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 惢 is uncertain. It visually consists of three 心 (heart) components, but this may be a later formation rather than an original semantic compound.
Three hearts stacked together suggest intense emotion or suspicion, but the actual meaning is unclear.
For サ, imagine three hearts whispering 'sa' in unison, like a soft sigh of doubt.