Though I'd add my perspective to this thread; sorry it it's repetitive, as we can think quite a like :P
For me, emotions are always present, just muffled. It's like a simmering fire, becoming oxygen deprived as I relentlessly hold them down. I've always like the dam analogy. Usually what happens is they're continually suppressed, and I don't react emotionally in a majority of situations, but one day, whether several months or potentially years down the road, depending how much emotional stress I go through, eventually that dam breaks and floods everything.
I remember one time when I was 11, I blew up at my 17 year old sister, and she was literally scared for her life. Her boyfriend (now husband) had picked me up and set me out of the pool, because we were having an argument on who got to use it how (My friend and I had just gotten in 5 minutes before they came out and were splashing; my sister wanted to tan and relax.) Him man-handling was the straw that broke the camels back so to speak, all I knew once I was set down was pure rage, I literally saw nothing but red, mentally and physically. My family had never heard me swear before, and I used every single word in the book and made up some of my own.. after a few minutes, I settled down, my sister had locked herself in the house and kept me outside. She was seriously scared for her life, and had called our mom. I ended up settling down, and just felt drained afterwards, the dam was empty, and I rebuilt the walls to hold the water back once again, and didn't blow up again for another few years. I couldn't explain myself or anything, I was kind of shocked afterwards.
Other than episodes like that, whether I break down sobbing or raging, I'm entirely stoic. I kind of think of myself as vulcan really. It's not that emotion isn't there, just suppressed in desire for intellectual stimulation. But, as well like Vulcans, I feel emotion 100x's more powerful than humans do. Vulcans were modeled after INTP's :P
I also think this is the reason I fall in love so hard and fast. It's something I only sometimes suppress, because part of me desperately wants that connection with someone, someone who can provide me the support I needm, and I can fully open up to. I dream of that, but don't know if I'll ever really trust anyone that fully.
Most of the time I feel pretty dead or empty, whenever something happens. The death of a family member, friend, anything like that. It's all irrelevant/meaningless.
Anyway, that's my ramble on emotion..