what happen exactly with yoona? 

is she really got an amnesia?

after she knew the fact that shinhye is her real sister

then she got an accident an coma

when she is in coma and lost her awareness

she had a dream about shnhye and what she always do to make her sister hurt

after she wake up

she had feeling guilty and she dont want make her sister hurt with her presence anymore

then she try to called someone before shinhye coming

SHINHYE:YOONA ITS ME...DIDNT YOU KNOW? she asked

YOONA:WHO ARE YOU? she pretend like she didnt know her

shinhye tears falling when she knew her condition

minho try to comfort her

MINHO:MAYBE SHE GOT AN AMNESIA he caress her shoulder

then someone suddenly coming

shinhyenturn her head and she was a shocked when she saw him

SHINHYE:SEUNGGI? yoona old ex boyfriend

SEUNGGI:SHIN...MINHO....he greet them

MINHO:WHAT ARE YOU DOING HERE? he didnt like it with him

but....

YOONA:SEUNGGI OPPA....she called him

SEUNGGI:YOONA YA...he coming to her

YOONA:I'M GLAD YOU COMING

seunggi caress her hair

MINHO:YOONA,YOU KNOW HIM? he didnt believe it what he just saw

YOONA:HE IS MY BOYFRIEND she nodded

MINHO:BUT SHINHYE IS YOUR SISTER,YOU DIDNT KNOW HER? he asked

yoona shake her head that she lied

then minho try to found out the doctor

and doctor said maybe yoona got a litle amnesia and she lost the part of memory that make her sick

so maybe thats why she just know seunggi

shinhye really sad when she knew the truth

5hen seunggi meeting her

SHINHYE:YOU WANNA BRING HER?

SEUNGGI:NE SHIN,I KNOW MAYBE YOU HATE ME BUT TRUSTED ME I STILL REALLY LOVED HER AND FELT REGET WHEN I LOST HER

SHINHYE:WHERE YOU WANNA BRING HER?

SEUNGGI:AMERICA,SHE CAN GET THE BEST DOCTOR THERE he said

shinhye felt confused right now

if she need believe him or not

but she knew yoona only trusted seunggi right now

she dont want make her more hurt 

SHIN