My grandmom has dementia? Please help!?

Your grandmother experienced a (brief) state of dissociation, which is often seen in dementia patients. Dementia is the result of damage to brain cells (neurons). Since the brain performs so very many functions, the symptoms presented when areas of the brain deteriorate can be quite varied. Her 'vital' signs really don't reflect what is happening within her brain, so vital signs can be perfect even if her behavior is bizarre or unusual.