感 sets 咸 ('all', also the sound) over the heart 心: everything reaching the heart at once — to be moved, to feel. The heart radical does its usual quiet work: wherever 心 sits underneath, emotions are happening.
感 feels everything: 感谢 (thanks — formal gratitude), 感冒 (catch a cold — 'feel the miasma', medicine's poetry), 感觉 (feeling/sense), 感动 (moved to emotion). 有感觉 ('has feeling') is how young Chinese describe romantic chemistry; 没感觉 is the gentle rejection. From colds to crushes to thank-you speeches, 感 is the heart registering the world.
All 咸 of it landing on the heart 心 — to FEEL.
感冒 'feeling the bad air' — catching a cold preserves miasma-era medicine in two characters.