I am becoming bitter and pathetic because I resent my friend's natural happiness

A friend of mine recently tried ecstasy at a festival for the first time, it was a great experience for her and everything went fine (she had it tested and did it with someone she trusts so no problem). Now its been a few days later and she is experiencing the ecstasy dip of lower serotonin levels. She is the type of person that has always been out going energetic and bubbly, its just her natural way. She has this thing about her that makes it easy for people to talk to her and guys often fall for her over this great personality. I've never had a problem with that, she's my friend because she is such an awesome person and I'm glad to have her in my life. What bothered me and is still bothering me is something she said during her dip. She began describing how she felt like sad when she was alone and even though good things were happening she just wasn't so much into it as usual. She said to me " I know this emotional low is coming and the best way to deal with it is to just think its my serotonin levels and that it will be over in a few days". The thing is when she described how she felt due to the after effect of ecstasy it perfectly described how I've been feeling everyday for the past few years. The thing that got me was that she said it would be over in a few days, that made me so angry and jealous. I felt so bitter that for her this was just a one off thing and that I wish I could just get over this feeling but it won't go away. I never wanted more to be like her where she never had this shadow hanging over her regularly. I know its selfish and self centered, I know I should have just tried to be there for her but I couldn't fully in that moment. I just want to feel happy and interested in things again. I'm trying so hard to push myself but nothing changes