This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
愱 combines 忄 (heart) with 疾 (sickness, rapid), likely forming a phono-semantic compound related to emotional distress or suffering. The exact historical development is uncertain.
The heart radical 忄 beside 疾 (sickness) suggests a heart afflicted by illness, leading to suffering.
For シツ, imagine a heart suffering from a sudden illness that makes it beat rapidly: the sharp sound 'shitsu' echoes the quick, painful pulse.