Sadness

Agony, anguish, broken heart, hurt, sorrow, dejection, dismay, homesickness, distress, dissatisfaction, and other terms are used to describe sadness. All of these feelings may manifest in response to unfavorable or unexpected events, or to changes in one's lifestyle.
Sadness frequently coexists with other emotions like rage, tension, guilt, grief, worry, or hopelessness. There are occasions when the other emotion may be so overwhelming that you fail to recognize your sadness.

Then how does sadness feel? It might alter how you physically feel. You might be experiencing a headache, a stomachache, or trouble sleeping.
Sadness can alter your emotional state as well. Perhaps you are sad, irritable, bored, or frustrated, or you just want to stay away from people.
However, acknowledging your grief and realizing that it's alright to be sad are indicators of a steady sense of wellbeing.

References (Example)
[1] <name>, '<title>' (online, <year>) <link>.
[2] BULB, 'Write to Earn. Read to Earn' (online, 2022) <https://www.bulbapp.io/>