The Espanyol defender passed away from heart failure while on a pre-season tour of Italy with the Catalan club at the age of 26.
Iniesta admits that he had "no feelings or passion" following Jarque's death, and that he sought help during that difficult period in his life.
"You feel that it's not you, that you don't enjoy things, that the people around you are just people," the 34-year-old, who recently left Barca to join Vissel Kobe in Japan, told Spanish television outlet Antena 3.
"You have no feelings or passion. You end up feeling empty inside and there is a moment that you realise that you cannot take it anymore.
"I had the ability to see that I needed to see someone to get out of that situation. The important thing is that in that period I never lost the spark."
When Iniesta scored Spain's winning goal in the 2010 World Cup final against the Netherlands, he took off his shirt and revealed a tribute written on his vest that said 'Dani Jarque - always with us'.