Eight days is not long. For my tongue surgery I was in hospital for two and a half weeks. You obviously still need a lot of pain control medication. I found the pain would die down and then flare up again. After my last surgery I was fine during my last days in hospital and then had a major flare up of pain after I got home and had to go to A&E to get it sorted out. I was not taking my medication properly. One they explained how to take the meds I was fine and eventually of course I could come right off them. I'm talking 2 - 3 weeks.

Good luck!

1996, ovarian cancer surgery + cisplatin and taxol.
September, 2007, SCC of left lateral tongue. Excision.
October, 2009 recurrence in scar tissue, T1NOMO. Free flap surgery from left wrist - neck dissection. 63 year old New Zealander. No chemo, no RT.
February, 2014. New primary in left buccal mucosa. Marginal mandibulectomy, neck dissection, right arm free forearm flap. T1N0M0 but third occurrence and some areas of concern: RT started 8 April and finished 19 May.