Hello, My Mom Has Been Experience "tremor-like" Symptoms In Her

Hello, My mom has been experience "tremor-like" symptoms in her brain and chest/heart. she said it feels like her brain and heart are vibrating whenever she is at rest (sitting, laying down, trying to sleep -- but not while driving or moving in a car) this has been happening for a few weeks now and each episode varies in length and intensity. Some things I read online indicate this may be Lyme disease but it doesn't appear she has any of the other symptoms....It's literally driving her crazy she says and I'm quite concerned. Have you ever heard of any one else with these types of symptoms and what could this be an indication of???