What causes this type of stroke & how long does it take to recover?

[groze5858]

My mother had an unusual type of stroke on Wednesday (10-12-16).  She is still in the hospital.  She can move everything legs, elbows, knees & she can talk coherently.   The issue is the dizziness, weakness and nausea.  She is eating and keeping food down as of 10-16-16.  She gets wobbly and dizzy when she gets up or wakes up.  She is starting to get up a little with a walker.  Why didn't my local er cat scan see the stroke & when put under observation in the local hospital the mri showed it and when she was transferred to another hospital & admitted their cat scan test showed the stroke?    Does the local ER need a new cat scan machine?  Why didn't the emergency room test for stroke right away?  I read they can give drugs to stop it or slow it.