Thank you guys for all your answers.
I tried to think once again what has changed over these 6 months, and here are a couple more observations. Like some people here, I've also noticed that i'm less subject to colds and flus, in fact during all the 6 months, i never fell sick, though there were many times i felt i was "on the edge". Before the experiment i used to have very weak health, constantly coughing and sneezing, also some chronic sinus diseases. At the same time that i went vegetarian, i also started taking cold showers every day. So these two factors (probably) were a lot of help in improving my health.
Also my overall emotional state has improved. I've always been quite stress-resistant, positive thinking and positive feeling. But compared to 6 months ago, i really feel more joy and peace every moment. But i don't think it's due to vegetarian diet, but rather due to some conscious work on my mental and emotional state.
The only thing that bugs me is sleep. I used to be able to sleep 3 or 4 hours a night for weeks and have no visible negative effects. I could get up whenever i needed to no matter how much sleep i had got. Now it's very different, if i don't get enough sleep for two nights, i feel really drowsy all the time and sometimes just cannot resist the urge to fall asleep.
Anyway, i've decided i will first get other areas of my life in order, such as waking up early, maintaining a proper sleep schedule, running every morning, etc. And after i take care of all other issues, i'll experiment some more with diet. Cause any positive effects of vegetarianism could be overweighed with negative effects of sleep deprivation and lack of physical activity.