yes I have heard of this before. often spirits from your past will come to greet you before you go.. so you know it will be okay. Is your mom afraid of dying? many that I know who have had this experience have been afraid to die. and it is their way of letting in your case your mom know that it is a good place to go to. that it will be okay.
she may be hanging on for your sake or your dad's sake... if you tell her it is okay to go she may go. My mom and I did for my dad.. it was time. he was so far gone with cancer it was just time.
also so the alertness often comes before the end.. a gift for you really.. a time to get to really talk to her one last time..
if you want or need to talk to me about this ... I will be glad to.. b10vamom AT gmail DOT com fix the email to normal format and you can reach me there. sorry was looking for GERD information.. found this for parkinsons.. my mom has it too.. and well saw your note.. and I hope I am not too late to help you.