Last few months, I feel always very guilty about random thoughts, and very afraid, if people would find out. For example, that I would hurt someone I love with all my heart, or when I was sick after a partynight, I assumed immediately I had an alcoholproblem where I otherwise rarely drink or like yesterday,I took a bath and had a fantasy about a girl other then my girlfriend where I acted on. And now that last one is haunting my thoughts again, where to I can't function normally. And when that happens I get locked up inside myself, trying to understand why I think those things, I get deeper and deeper, with more irrational thoughts. And its one after the other, how can I ever get out of this cycle.

I understand how you can spiral down into irrational thinking. I think quite a few people can. This thinking makes you a prisoner of your own thinking... as you said - Locked up inside yourself. However - You recognize this, and with this knowledge you can change our thought patterns!

The conscious mind feeds the sub-conscious mind, and then this feeds back on itself. You think of some scenario in your mind, and your sub-conscious mind starts to manufacture all the evidence you need.

To break this, you have to catch yourself when you are being negative minded.

Give your sub-conscious mind something positive to work on. Imaging yourself being the best you can be, or behaving in an honourable way. Your thoughts will start to change over time.