Hi Morningsun,
As I understand it nervous energy is energy that is ungrounded. Energy centres are not balanced. In this condition, one is wide open to all energies. Thus not only is your own energy not flowing in a unified way, but you are also vulnerable to whatever energies are around you, hence the energetic twitches of not being able to sit still. As the body is a potentially unified consciousness, stilling the mind is crucial. This can be assisted by grounding yourself on a regular basis, daily if you can, as you rise with the morning sun 
If you do a net search you'll find numerous methods of grounding. Sending out a grounding cord or pillar of light to the centre of the earth, and also upwards to as far as your imagination can take you is a way of anchoring your energy. I send a pillar of light to the sun, and downwards to an imagined crystal of my choice in the centre of the earth.
Doing gardening helps enormously, or being around trees or water, where there is a higher level of chi in the atmosphere, to walking the dog, or just being around animals.
Once when a series of psychic attacks were literally frying my nerves and making me twitchy and dizzy, so much so I feared crossing the road, I did an "emergency" grounding in my lunch hour at work, by leaning against a tree with my shoes off. Worked a treat. So nature is of great assistance. Send all the nervous energy back into the ground and give thanks to Mother earth for her assistance.
Talking of cystals, I find smoky quartz very grounding, but again you have to check out which crystals you are attracted to. Just having a grounding crystal on your person helps too.
If you are into Yoga, you could do what is generally called a salute to the sun. Most Yoga books have this exercise, as it works the whole body in a series of linked movements, helping the flow of energy in your body. 5 to 10 minutes of this every morning will have a significant impact. Always finish with a series of relaxing breaths to ground you.
Another thing you could try in tandem with this, is working on energising and balancing your chakras. With practice, you will get to feel which chakras need work on the most. With nervous energy, it is usually the root chakra (base of the spine) and the crown chakra (top of your head) that need most work. But of course, the condition of the heart chakra could also be the heart of the matter. Work systematically through each chakra everytime. In my limited experience I have found it is important to take your time, ensuring that you will not be disturbed during your energetic exercises.
Finally, meditate regularly - daily if possble. There is a Taoist stillness meditation that is deceptively simple but very effective for busy city dwellers like myself. Asking your higher self and your guidance, what the root of the nervous energy is might be a question for when you are meditating. You may find doing this first will get you still enough to contemplate other complimentary methods. Check out http://www.tomkenyon.com/articles/taoiststillness.html if you feel inclined to try this.
All in all, I think making a conscious decision to get off the whirly-gig on a regular basis to just work on yourself is the key thing. Hope this helps in some way.
V
P.S. Swimming regularly, followed by a sauna, will tone and detoxify your body and have a unifiying effect on your energetic centres. I think sauna's are great places to meditate.
The truth, the whole truth, and nothing but the truth.
But that's when it began. Throughout the entire movie I experienced weird fluttering and chill spasms eminating from my heart chakra. 