• 患者かんじゃ — patient (a sick person)
• 患うわずらう — to be ill; to suffer from
• 急患きゅうかん — emergency patient
• 患部かんぶ — affected area; injured part
• 疾患しっかん — disease; medical condition

This kanji is built around the idea of something troubling the heart. That “burden” can be physical — like illness — or mental — like worry. So 患 is used for being ill, suffering, and also affliction.