Bipolar mom is having seizures and tremors?

My mom is bipolar and addicted to ritalin and previously an alcoholic. She has just noticed she has tremors - she shakes when doing certain movements. Also, whenever she stands up quickly she feels all warm and blacks out like she is doing to faint. She has fell down and had seizures several times after standing up. What do you think could be causing this? She is on a variety of bipolar meds but hasn't changed them in a while so I dont think this is the cause. Thanks!