"Mommy's brain is broken, kind of"...explaining things to a 4-year old so he understands them without being scared

  Last night Nixon had an extra late night. He stayed up until almost midnight! He was in bed with me watching a movie on TV being good and quiet. Since Mac was working I was okay with a slumber party/movie night in our bed.
   I had to go downstairs and take my medications for the night. I told Nixon I as running downstairs to get my meds and Nixon says "Mommy, I need meds too. I am sick." *sigh* This is when I have to explain to my 4-year old that my medications aren't for an illness but for my "broken brain".
me: Nixon, I take medication because my brain doesn't work right not because I'm sick.
Nixon: You brain is broken?
me: Yeah, kind of. It doesn't work like it's supposed to. The medicine helps it work like a regular person's brain. Like yours does.
Nixon: Because my brain isn't broken?
me: No, baby, your brain isn't broken.
Nixon: How did your brain break?
me: Oh, well, I didn't have a good childhood and my brain worked differently to help me deal with it. Now my brain thinks that's a proper way to function.
Nixon: But you brain is broken!
me: Yep, it doesn't know it is, but I realize it doesn't work like it should.
Nixon: Can I see you brain?
*I get on the bed so he can look at my head*
Nixon: I see it mommy! I see your broken brain. It's cracked right here *points*
me: Wow! You can really see it?!
Nixon: I'm going to kiss it, so you feel better. Then you can go take your medicine and be a good mommy for me, okay?
me: *almost tearing up* Okay, baby.