You have been doing "neigong" for years and perhaps do not know or recognise it -- its Sanchin & Tensho.
The 'problem' is, it was and perhaps still is, taught as a pure physical conditioning routine with combat applications grafted on, and so the "internal" ('neigong') aspects got lost along the way.
When doing it, reduce your tension by half and instead of concentrating on the breath coming out of your mouth, internalise your thoughts and focus on your internal organs on the in-breath and imagine the breath coming out of your skin on the out-breath.
After some practice, you should notice that your body felt as if it 'shrinks' a bit on the in-breath and 'expands' on the out-breath. The 'shrinkage' will give you an awareness of your muscles squeezing on the bones. After more practice, you can hold the tension with any combat-body-configuration and still feel no strain whatsoever and to the on-looker, no apparent tension. So now you can truly fight with Sanchin.
And here is one little 'thing' you may wish to consider -- spend 5-10 minutes (whether sitting or standing) and just think or concentrate on your finger tips and while keeping that concentration, do the Tensho kata. When you are better, go up to the palm and eventually the whole body. At this stage, you will see Tensho and Sanchin in a whole new 'light' and then go back to read that little piece in Wikipedia again or any of those books Eyrie recommended. Reading them before will be guite meaningless to you.
Call me again in a couple of years' time. Meanwhile
Perhaps a little clearing up on "neigong" and "chigong"
About 40-50 years ago, the term neigong was more commonly used than chigong because the majority of practitioners were martial artists; neigong being internal training for martial arts application. Later as MA itself became less wide spread due to the influence of Western science and technology, people began to concentrate on the health by-product aspects of neigong and since it merely develops the chi without any martial arts application, chigong was used to distinguished it.
The common denominator is of course the development of the awareness of the dynamics chi plays in the body's processes; the point of divergence comes when the martial artists use this awareness for bone, tendon and muscle development and all these are then combined into one coherent practice when doing the kata; in your case the Seisan kata. The 'secret' is in the kata?