Is lying on the bed with laptop on one side a very bad posture?!

As you are trying to use a laptop in that position, you are probably twisting or straining in some way that is not having a positive effect on your posture. The problem is that you get so engrossed in what you are doing that you don't notice if you are feeling stiff or uncomfortable. If you have to do this - find a position that is comfortable, where your spine is supported and that you are not un-naturally twisting or straining your neck and shoulders, but take a break every 10 minutes or so and stretch out a little. Ideally, you should sit at a desk to use your laptop, as this means that your back, shoulders and neck are in a more supported and comfortable position.

http://www.chiropractic-uk.co.uk/

I hope not, I do that all day everyday.