Unfortunate result, lacking energy - you start to get passionate (6)
I believe the answer is:
sultry
'passionate' is the definition.
(I've seen this before)
'unfortunate result lacking energy you start' is the wordplay.
'unfortunate' is an anagram indicator.
'lacking' is a deletion indicator.
'energy' becomes 'e' (physics symbol as in E=mc2).
'you start' becomes 'y' (I've seen this in other clues).
'result' with 'e' removed is 'rsult'.
'rsult' with letters rearranged gives 'sultr'.
'sultr'+'y'='SULTRY'
'to get' acts as a link.
(Other definitions for sultry that I've seen before include "(Of weather) hot, humid" , "Hot, close (weather)" , "Sweltering - arousing passion" , "Sweltering, close and oppressive" , "Oppressively hot and humid" .)