I think this means you don't feel safe with whatever it is you have manifested - work on your core issue of safety.

According to the Ninth Density Plaedian Collective channelled by Wendy Kennedy http://higherfrequencies.net/, there are only about half a dozen core issues - ABANDONMENT, SEPARATION, TRUST, CONTROL and SAFETY. They suggest asking yourself questions about the situation and just allowing your subconscious to guide you to answers - this may take several times of asking but your subconscious wants you to know the answer. They suggest you write it out to just get it through the body.

The reason I feel this fear is (fill in blank) ... The thought that created this scenario (fill in blank) ... What thought do I need to replace that thought with .... (and then pulse that thought out) How does this situation serve me? This is a big one as every "negative" situation serves us in some way - an example would be not allowing ourselves to find a relationship because we feel unsafe in a relationship or we fear separation.
Why have I created this scenario .... ? What am I resisting (resistance IS fear, according to the Plaedians)? What beliefs have created this situation?

Once you have awareness about where you are vibrating in relation to this situation you can flip it into what you do want. So the awareness leads to a point where you can say - yes, I can see why I have created this and therefore I can see the thoughts I need to think in order to turn it around. Or increasingly you just think what do I want to create, what would that feel like and just feel that.

Bear in mind that there is nothing wrong with you - you are completely perfect, it is just a programme you have running that is covering up the perfect you. My guess is that it is a SAFETY issue so work with affirmations - I AM SAFE. IT IS SAFE TO HAVE/BE THIS THING (whatever it is, you don't say).

This advice isn't something I've just made up by the way - it is almost word for word from a mp3 session from Higher Frequencies - you might want to check out their website for further details. The 2013 mp3 is quite expensive but I have listened to it several times and got a lot from it.

I will not answer this question from a spiritual point of view but rather from a factual point of view, because I have felt like this a few times before. Just like people usually have a fear of failure, many people also seem to have a fear of success, which seems to be what you are experiencing at the moment.

Fear of success means that you feel that you are actually not ready to partake the new responsiblities that are going to come together with the new item that you have desired/manifested. You somehow just feel that you will screw up the whole thing.

For instance, if you have just got into a relationship, you would have completely different worries from before you had the relationship. If you have just gotten a new job, you might feel that you are still not capable enough for that particular job and might screw up everything and land back in square one.