"Mentally, it took its toll," Kardashian tells PEOPLE of the tragedy. "But it wasn't about me. I realized how much it was about [Lamar] so I didn't think twice about it."
"Normally, when I'm going through stuff, I have my release of energy or stress at the gym," says Kardashian, 31. "But I literally didn't leave the room for a month. I wasn't sleeping as well. I went a week without showering."
Continues the star: "I was stuck in a room with my thoughts. My mind didn't have that release. I was like, 'I can't breathe!' "
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For much more from Khloé Kardashian, including exclusive photos, pick up the new issue of PEOPLE, on stands Friday
"I had to switch gears," says Kardashian. "I was like, 'I know I'll get back to the gym, I know I'll get that release, but for now, what's my therapy?' "
Continues the Strong Looks Better Naked author: "I had to remember that even though something tragic was going on, I still needed a few minutes. I was like, 'Okay I need to take a shower.' Just the little things make you feel so much better. I had to learn to [take care] of myself."
Kocktails with Khloé premieres Jan. 20 at 10 p.m. ET on FYI.