Brain damage from a heart attack???

I don't understand how my mom can make it all the way on a flight for life to Rapid City, SD and follow commands after coming up from the CAPH (?) lab and then less then 24 hrs later she isn't responding.  She has never had heart problems before this incident and is 63 yrs old.  If you need anymore background info let me know.  The heart attack happened on saturday the 17th and since sunday the 18th she hasn't responded to commands, but will open her eyes when we talk to her.  However when she does open her eyes there isn't anything there.  Any ideas ?  The nuerologist said she had a series of mini strokes or lack of oxygen that has caused brain damage.  THis was his interpetation of the test results from Thursday's EEG..  Another one is scheduled for Tuesday to see if there is any improvement.  Any information would be highly appreciated!!!!!!!!!