Great thread! I too am having the same thoughts.
I'm actually taking a trip home tomorrow (it's about a 4 hour drive) and have been thinking about this. I update my family about how I'm doing over the phone, but I am looking the best I have in years (lost 50 pounds!) so I know it's hard for them to comprehend that I have less energy than before.
Yesterday I decided to email them information about MS fatigue. I found a great site that explains it simply and I told them it was important to me that they understand. This morning my mom got back to me and said yes, it is hard for others to understand but reading about it helped a lot.
Long story short, I feel better going home tomorrow knowing that my mom won't ask me to join her in her 4km walk, my sister won't drag me to the mall for hours, and if I need to have a midday nap, they will understand why now and not tease me about it (well, they probably still will, but that's ok.)
Diagnosed with MS April 2006
Longstanding anxiety and depression
Currently on Betaseron