Dementia
noun, の adjective
If you seem stupid and shocked all the time you might have dementia. It makes it so everything is unfamiliar and confusing, so you can't help looking silly and confused all the time.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
祖母の痴呆が始まったんです。
My grandmother is starting to get dementia.