QUOTE
I find that when i'm in my lessons when I come out my neck is killing me and it travels up my head and I end up with a headache all night, and i'm starting to notice this with practise too.
:-(
Could you be a little more specific when you say neck?
It is almost certainly tension - mental tension leads to physical tension leads to mental tension... This is why things like the Alexander Technique or tai chi are good. They help you recognise and release tension in your body. Break the cycle. Especially at times of stress!
Personally I find my mental stress manifests in my trapezius, between my shoulder blades. I used to get it a lot when I started driving on motorways (and I'd get cold hands from the tension). After more experience driving and concious relaxation I've managed to drive for hours without that particular ache.
More recently I've have a stiff neck when running a long way. I realised that I have a new tendency to stick my chin up and out a bit (I think because that's the position my head is in when I'm cycling). I'm wondering if you do the same?
It's really interesting how almost all physical tension has a related emotional element. I have a friend who is quite defensive. She takes things a little too personally and seems to be looking for a fight. Her big postural problem? She pushes her chin out far to far. It's almost a "come and have a go if you think your hard enough". Unsurprisingly to me, she gets bad migraines.
Another friend from university was a very shy guy. He used to be bullied at school. Now he was a tall guy, 6' 2" at best guess. But you'd never know it. He slouches, haunches his back, folds his arms across himself in awkward ways. Anything to make himself look smaller.
Not wanting to get pseudo-psycho-analyst on you, but do you feel you have anything to prove in your piano classes?
Hopefully it's just a physical posture issue, and you can fix it with a bit of awareness - ask your piano teacher to observe your posture and tell you if they see any tension. Maybe go and get a decent massage - if you are practising every day then you're probably compounding the problem, and a massage may help to reset things.
If it is emotional/mental, then fixing the physical problem will help, and may be a great step in resolving the mental problem. But if the root cause goes un-resolved, then you can expect the problem to manifest itself again, possibly in a bigger badder way.
Hope that is some food for thought!