Withdrawal/Overdose
Chronic opioid/benzodiazepine/zolpidem (Ambien) use
ETOH abuse - may not experience tremors in ETOH withdrawal
Polypharmacy
NSAIDS - may be taking multiple
Long term ASA
Steroids
Sedatives/Psychoactives
Anticholinergics - many OTC
Meperidine, cimetidine, ranitidine, TCAs, antiparkinson, antipsychotics, diphenhydramine
Dietary - teas, supplements
Long term ASA
Meperidine, cimetidine, ranitidine, TCAs, antiparkinson, antipsychotics, diphenhydramine
Dietary - teas, supplements
Other
Cardiac Ischemia - no chest pain needed
Seizure v Post ictal
Urinary retention - uremia
Fecal impaction
Occult mesenteric ischemia
Electrolyte abnormalities (e.g. Ca/Mg/Phos)
Altered mental status 
Sedation 
Extrapyramidal reaction
Tremor
Catatonia
Dizziness
Insomnia
Focal neurologic deficits