By Tanya Khovanova
Answer: NECESSARY

This puzzle was inspired by by Derek Kisman’s fractal word search, In the Details, which contains a crypto word search as one of the steps.

First we solve clues, noticing that the answers are in alphabetical order:

It ends your sleep (5) ALARM
A feeling of unease (7) ANXIETY
The end of the world, as brought about by horsemen (10) APOCALYPSE
Fear of water (10) AQUAPHOBIA
Insects in the stomach when scared (11) BUTTERFLIES
It conquered fear and crossed the road (7) CHICKEN
This word describes Sunday in a Hungarian song (6) GLOOMY
Shuddering fear (6) HORROR
A deviation in signal pulses (6) JITTER
Sad feeling of singles (10) LONELINESS
A moaning ghost living in a bathroom (6) MYRTLE
Adjective describing a fallacy attributing human emotion to nature (8) PATHETIC
His glass is half empty (9) PESSIMIST
Overachiever’s concern (6) STRESS
Type of denial of service attack (8) TEARDROP
Hamlet or Macbeth (7) TRAGEDY
Earthquake harbinger (6) TREMOR
Calming root (8) VALERIAN
Word to describe a baby or siren (7) WAILING
Shed tears (4) WEEP
Producer of wrinkles (5) WORRY
Scary undead (6) ZOMBIE

Looking at the word search table, one might notice that the letter frequencies are off, and overall it looks encrypted. We try a substitution cypher. A good place to start is the word PESSIMIST, as the string XXY?YX can be found only in one place. After we place PESSIMIST, it is easy to place STRESS, LONELINESS, and APOCALYPSE. After that the table can be deciphered.

A V M Y R T L E W E E P E
C E N E R R E A L I Y E S
I C T E A R D R O P D S P
T N H A F Z O M B I E S Y
E Y S I Q E C W T N G I L
H M S I C U A V I O A M A
T O E N C K A L A L R I C
A O R L E L E P A D T S O
P L T R E N T N H R H T P
E G S R O M E R T O M C A
S E I L F R E T T U B L A
W A I L I N G R E T T I J
N P N I N E Y T E I X N A

Extra letters (in yellow) spell A VENEREAL INFECTION CALLED THE CLAP NINE. This clues GONORRHEA. The last step is to encrypt GONORRHEA using the same substitution cipher. The answer is NECESSARY.