One of the greatest and most important lessons I have learned during my grief process is to not judge myself. Because I am a person who is normally happy and joyful, I spent so much time beating myself up for the sadness--and sometimes anger--I felt while grieving. It was such an unnatural state for me to be in, and I thought I shouldn't be in it. I couldn't accept what I was feeling; I didn't even want to believe grief was real. Honestly, I believed that grief was something I could choose to experience. So, I figured if I chose not to grieve, I could be my happy, joyful self and just move on.
In truth, until you acknowledge and accept that grief is something that has to be accepted and felt, as it is natural and essential to healing from a loss, you will not heal. You have to feel it all, acknowledge it all, and then yes, in your own time, let it go! Handling mental pain is never as easy as dealing with a physical ailment, where a doctor can diagnose the injury, prescribe a remedy, and tell you when you should be "good as new." However, just like your body, your mind requires a healing method of its own. Not following a prescribed healing method will only prolong your grieving process and increase your pain.
So yes, give yourself permission to feel all your feelings: the good, the bad, the ugly, and anything else that may come along. Express them to a trusted friend or professional. Come to terms with the fact that you can't control everything that happens in your life, especially a loss of a loved one. Be gentle with yourself and with those around you. Take a deep breath. Do whatever makes you happy, even if it's just for 5 minutes (or 5 seconds!). Take especially good care of your emotions, thoughts, and feelings. Act as if you're healing from a broken leg and have a cast on: you would use some crutches for awhile and take extra care of how you were walking, because you would know that eventually, you would be healed and be free of the pain, the discomfort, and the confines and restrictions of the cast. Grief acts just like a cast: confining you to sadness, restricting your daily life. However, like a cast, grief doesn't last forever. In time, your grief will no longer hold you back or weigh you down. In time, I promise that you will free yourself from grief's grasp.