Why do I have swaying/floating feeling after completing 10 day Vipassana course?
Yes, it's alright that it's happening (assuming you didn't somehow hurt yourself in an odd way). What you are describing is a normal occurrence at retreats of many varieties, not just Vipassana. They are simply symptoms of prolonged concentration, the degree and type of which are determined by your unique body, mind, and karmic history.

Sensations of lightness, swaying or rocking, tears, tingling, heat, chills, intense joy, bright images, etc. are all common occurences of Piti (also known as Rapture). Piti occurs when a yogi concentrates in the right way for an amount of time. Piti's effects are temporary, and will fade with time, depending on how much and how deeply you experienced it. 

You're having the opposite reaction most have to these things - many yogis get attached to Piti and never go beyond it, or stop going deeper because they think they've reached Nibbana. So you're ahead of the curve in knowing that these pleasures are also Dukkha. You're having an anxious reaction to it, which in turn causes additional problems like trouble sleeping, which in turn causes more anxiety, panic, and stress in an endless feedback loop. What we resist, persists. Surrender.

I've personally experienced what you're describing many times. It will pass. You may also be experiencing a new, deeper awareness of your body that you haven't had before. Your mind is now more clear, focused, and observant - it's no wonder you're experiencing new strange things. That's pretty neat! A shift in perspective may be all that you really need.

Your feeling of lightness may be akin to the early stages of what is described in the suttas and by monks as the power of levitation. ;) Just try to let go, stop worrying, and enjoy these new things for now. Get back on the meditation cushion. Observe them just like any other meditation object, investigate them. Where exactly is the sensation? What makes it so insufferable, in terms of experience? Does it have an essence? Does it change? When does judgement arise, before or after the sensation?

Hope you feel better, find peace, and liberate yourself from this suffering.