I understand you my friend. Actually, there is always an underlying reason. I am feeling the same right now. My job is great, i like the subject, i could say that my supervisors really like me and trust me, but i feel sooooooo much pressure...I provoke that to myself and i don´t know why..I am quite new, in the sixth month of my project, and i just started to feel the pressure. I have to present 2 papers in a conference, in two months..And my personal target is to submit 3 papers within the first year. Maybe it is too optimistic or crazy, i don´t know, but i have a constant feeling that i should not betray the trust of my supervisors. I have that feeling all the time..And you know, when you feel pressure, you can´t perform like the way you can. It is a vicious circle. And when my bosses suggest me to make some corrections in the papers, although i know that it is normal, i feel like i do something wrong or that i am not good enough for this. The last month i don´t recognise myself cuz i used to be very cool and confident. So you are not alone man, i think that i suffer more!!!!!