Agitation felt when all the others lose their head? (12)
I believe the answer is:
restlessness
'agitation' is the definition.
(restlessness is a kind of agitation)
'their head?' is the wordplay.
'their' becomes 'restless' (I can't justify this - if you can you should give a lot more credence to this answer).
'head?' becomes 'ness' (ness is a headland).
'restless'+'ness'='RESTLESSNESS'
'felt when all the others lose' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for restlessness that I've seen before include "Unease" , "Inability to relax -- lessen stress (anag)" , "Inability to keep still" , "Quality involving constant activity" , "Agitation" .)