Muthukumaran
Hi James,
I know it's too late reply for you but I have read your question(or doubt) just now. I am 29 year old now and I have been doing Shirasasana for more than 6 years. I would like to provide some information to you.
If you do Shirasasana regularly you can feel that you are someone special and someone different from normal people.
You must have experienced that your memory power got increased, you feel happy for the whole day, gained tremendous energy, increased self confidence, things happening as you think, never caught cold, no eye problems, no ear related problem, and so many.
One thing you don't know is that you are very lucky because somehow you came to know about Shirasasana.
DOs and DON'T DOs:
1. You should not do this asana without consulting with a Guru(Yoga Master).
2. Before do Shirasasana you must stretch and warm up you body.
3. You should never do this asana more than 5mins(I suggest you 3mins).
4. If you don't feel enough for 3mins you can do it again for 3mins but you must have a break. To say exactly if you want to this asana for 9mins you must take break for each 3mins.
5. You should not stand up immediately after 3mins. I mean, when you completed 3mins of standing you have to bring your legs down but you should not get up immediately. You must lie down or sit down for at least 30secs then slowly get up.
6. Important: Once you done with Sirasasana you must do "YEGAPADHA ASANA" or "NINRAPADHA ASANA". This asana will balance the blood circulation to all the parts for ur body from your head.