What Causes Head To Spin While Lying Down?

In Dec 2010 during a surgery they did a lumbar punture to check my pressure.( Ive had Chiari Decomp Surg) surgery was for disk fusion....my pressure was over 300..for the past 5 days when I lay down my head spins like I was going round and round and sometimes when Im walking I feel unsteady...should I be too concerned?