Since Thursday yours truly’s laid up — with this? (6)
I believe the answer is:
asthma
'this?' is the definition.
The definition suggests a singular noun which matches the answer.
'since thursday yours truly's laid up' is the wordplay.
'since' becomes 'as' (I've seen this in other clues).
'thursday' becomes 'Th' (common abbreviation).
'yours truly' becomes 'am' (I can't justify this - if you can you should give a lot more credence to this answer).
'laid up' says the letters should be written backwards.
'am' in reverse letter order is 'ma'.
'as'+'th'+'ma'='ASTHMA'
'with' acts as a link.
Can you help me to learn more?
(Other definitions for asthma that I've seen before include "Respiratory problem" , "Respiratory condition" , "Distressing ailment affecting breathing" , "breathing problems" , "which leaves one breathless" .)