Am I nuts swimming in this? Yes (7)
I believe the answer is:
'this? yes' is the definition.
The definition suggests a singular noun which matches the answer.
'am i nuts swimming' is the wordplay.
'swimming' indicates an anagram.
'aminuts' is an anagram of 'TSUNAMI'.
'in' acts as a link.
(Other definitions for tsunami that I've seen before include "Large ocean wave" , "wall of water" , "Large tidal wave" , "Seismic sea wave" , "Long sea wave" .)