Concerned about the Power of Belief

Hi friends,

I was hoping someone could shed some light on a worry of mine that I've had for over a year now.
Since my teenage years I have always noticed the synchronicities and power of the law of attraction-- that what you think about often will bring to you people, materials and opportunities to manifest it with.
However as my studies deepened and the synchronous events increased, I started worrying about what my negative thoughts might manifest as well. To my horror, much of what I was thinking about manifested, and I was left wondering whether they were events I was having premonitions about, or if I was manifesting these events myself, by having thoughts about them.
This led to a bout of insomnia and 2 terrifying panic attacks that I wish never to repeat.
Can your thoughts manifest absolutely anything? For instance, if I worry that a favourite food of mine will give me an allergic reaction, can that manifest? Sometimes I find myself so concerned about these things that I am constantly checking myself in the mirror to make sure I haven't broken out in a rash! I know this sounds ridiculous, but from past experiences, thoughts really do create your reality.

Any advice would be so appreciated.
Thankyou.