I can be the same way. My therapists have always been amazed at how calmly and rationally I can talk about the grisly details of my past without a plicker in my eye. I learned at a very young age that feelings are not to be expressed. Feeling is bad basically.

Over time though I learned to accept and allow my feelings. Still when situations arise where I am in immediate danger, my feelings get pushed far away and I am able to calmly and rationally find a solution. But after the immediate danger the feelings now kick in and are extremely overwhelming. I think it has to do with my black and white thinking or something of the sort. As in my life it's always to the extreme, either too much or too little.
Therapists have been able to help me unlock the emotions. I cant control them anything like I used to be able to but I was able to finally feel joy and fun and peace and fear and pain, all of the emotions. While they are overwhelming at times, it's wonderful to be able to feel when you never feel anything.

If you're not with a therapist I highly suggest you find one, they can help you break the barrier and help you to allow yourself to feel again. I stopped therapy too quickly to learn how to deal with the overwhelming emotions but I actually cry at commercials and chick flicks now (not saying you will but it's NEVER been something I've done before, I never felt anything about anything) I'm able to feel angry toward those who deserve it, I'm able to feel happy when life is going well, and even when it's not I can still feel happy. The problem with not feeling your emotions is that when you block your emotions you block them all, the good and the bad. And on the best day of your life you still can't feel happy.

You can work through it though, with therapy and time it can get better. Best of luck to you

ETA: Being in therapy isn't about them changing you, it's about them giving you tools and techniques to apply to yourself so you can change yourself. Example: When I went through a horrible anxiety phase my therapist was able to give me positive affirmations to use which helped my sleeping which in turn helped my anxiety. They don't change you, they just give you the tools to change yourself.