Every new or unique experience is unsettling.  There is nothing by which to calibrate the event or its implications.  However, for the women who had come to the tomb early on resurrection morning, joy grew up alongside their anxiety because they knew that the Lord Jesus Christ was not dead any longer.
 
They had seen the exposed grave and had believed the words the angel spoke to them, promising that Jesus would soon meet His disciples again.  So, they had the joy of hope.  That spurred them to go back to give the men the wonderful news; and because of that, they ran.
 

The disciples had arrived at the rendezvous point, a mountain in Galilee.  Jesus had told them to meet Him there after the resurrection (Matthew 26:32).  The message was reissued by the angel at the tomb who commissioned the women to remind the men (Matthew 28:7), and was confirmed by Jesus Himself as He met the women when they left the burial site (Matthew 28:10).  Wonderfully, the disciples did not ignore the command.  They obeyed.
 

Matthew chooses to end his account of the earthly life of Jesus with this 'great commission'.  The eleven remaining apostles were present - Judas the betrayer was dead (Matthew 27:3-10) - even though some of them were really not sure what was going on (Matthew 28:17).  Having clearly stated the basis of His authority (Matthew 28:18), Jesus gave them instructions for their lives' work, and the work for all of the world-wide Church until He returns.