You can handwash gently in cool water and it will be fine. Then you can block it to get it's nice shape back. Hot water and a lot of agitation will possibly hand felt it though.
If you machine wash wool or other natural fiber that says handwash it will probably felt or at the very least shrink and look fuzzy. Machine washing a cotton that says handwash may damage or shrink it. Personally I wouldn't take a chance with something I put all that work into.