Tachycardia? Perhaps just high blood pressure?
If it’s fast when he’s sleeping then maybe he has obstructive sleep apnea.
Maybe he has a heart disease.
@Liver@BCS Seeing as how he's an artist and doesn't seem to be the fittest, it could be a combination of chronic stress from the FMC moving in/life or whatever and his general poor fitness that resulted in the tachycardia. I don't think it's ataxia because he doesn't appear to have problems with coordination, speaking, or walking.