anguish, grieve, ignorant, foolish
忳 centers on a troubled state of mind: deep anguish or grief, and by extension a kind of ignorance or foolishness that comes from being emotionally overwhelmed.
忳 combines the heart radical 忄 with the phonetic component 屯, suggesting a heart burdened or blocked, which aligns with the meanings of anguish and foolishness. The exact historical development is uncertain.
The heart radical 忄 beside 屯 (which can suggest something sprouting or struggling) paints a picture of a heart tangled in painful growth: the anguish and confusion of grief that can make one feel foolish.
For トン, imagine a ton of grief pressing on your heart: ton -> トン, and the weight of that anguish makes you feel ignorant and overwhelmed.