I have had all tests done except ct, fmri, spect to rule out the cause of my severe cognitive impairment and dissociation. should i have these done?

Hard to say: All tests should be based on a need suggested by a thorough history and physical exam. The tests you mention are unlikely to provide much information unless their need is suggested during evaluation. Sometimes psychoeducational or neuro-psychological testing is more likely to provide help in such a circumstance.

Psychiatric eval: Hopefully you are not attempting to manage your own evaluation, and are working with a psychiatrist and/or neurologist. These physicians are much more familiar with your case than we are, and can make the most appropriate recommendations. Functional imaging may well be part of an extensive evaluation, if you're in a tertiary setting. Neuropsychological testing may be useful also.