Tremor sensation when waking?

I've been on Focalin for about 2 months now and I've noticed over the last couple weeks I frequently have a weird internal tremor/vibration sensation inside my entire body when I first wake up. It's a sensation sort of like shivering but very subtle, without any actual physical tremor or muscle movement as far as I can tell. It will continue for several minutes if I just lay in that half-awake state, but as soon as I get out of bed it's gone. I'm wondering if this is related to ADHD medication. It goes away the instant I roll out of bed or sit up, so I'm not super worried about it, just wondered if anyone else had encountered anything similar.