The most common and most likely answer to this crossword clue is the 8 letter word DEMENTIA
I've seen this crossword clue in Financial Times
D
E
M
E
N
T
I
A
More clues leading to the result DEMENTIA
- Time and energy primarily needed for treatment of this condition
- Mad teen stupidly swallows one, making trouble for older relative?
- Dine with mate suffering form of insanity
- Detain me improperly, making problem for head
- A failing of powers of matinee idol’s second cast?
- Aide moving outside intended to avoid a complaint
- Doctors detain me for insanity
- Unfortunate condition of Parisian I meant to resolve
- Silverless repeat lifted into unhesitant goddess’s sad decline
- Somehow detain this writer coming in — there’s a medical disorder
Buddy explains!

The straight part
We know that "this condition" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case this condition = dementia.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does DEMENTIA mean?
DEMENTIA noun- A progressive decline in cognitive function due to damage or disease in the brain beyond what might be expected from normal aging. Areas particularly affected include memory, attention, judgement, language and problem solving.
- Madness or insanity.