Strange feeling accompanied by wobbling?

[Salatier]

Hi, I'm very new to this, and have begun trying to practice ...samatha? i hope that's right... by sitting and counting my breath, focusing on the point of feeling in my nose, all that stuff. I've done this once or twice a day for 4 days in a row now, each day the time of each sitting has increased.
Today i sat down just as i came home from school to begin, and everything seemed to be going well. I quickly became very calm feeling, when suddenly i felt a little panicky. I tried to stay focused but eventually, as a numbness feeling was felt throughout my whole body, i opened my eyes and changed my position, and it was all over immediately. It was strange, but i didn't think too much of it as i was no longer feeling panicked, and i still don't know what it was. But then, tonight, i just went to try again and was able to hold my concentration longer than before, probably around 15 minutes. After these 15, i started to feel the same numbness i guess, but without the panic. Remembering before, i held my concentration and stayed motionless. What felt like seconds later, i started to feel a little dizzy, and felt like i was wobbling. I started to get a little worried, fearing i had gone out of my limits and opened my eyes again to stop. I looked at my clock and i had been doing this for nearly a half hour, what felt like just over 15 minutes.

Does anyone know what this could be, and if it is bad? If i encounter it again tomorrow, what should i do?

ps Sorry, i know this post is unnecessarily long, i do that a lot...

[Reductor]

Meditation is an adventure: unexpected things happen. But there is nothing physically dangerous about it, so relax cause you'll be alright.

Be sure to sit with your back straight. Keep hips level with, or a little higher bit than the knees, so that you are not physically strained. Keep the head in a neutral forward facing position.

Because you are working so.hard to maintain concentration it seems possible that you are becoming tense. If you become tense, and are concentrating, your breathing may be slower and shallower than it should be. So physically relax as much as you are able while remaining up right, and breath easily.

Samatha or calming meditation should be relaxing. Concentration is not the forceful narrowing of your attention, it is a gentle turning of your attention toward your own body.

Gentle. And gradual. Meditation is a cultivation of your own mind, like the cultivation of a garden: daily, and for months and years.

Keep at it.

[Salatier]

Okay, thank you very much! I think i may have started to get tense, so that makes sense.
Thanks again!