1. get other people involved. get them up on skype or work on a server with them. it's a lot more encouraging when you aren't alone
2. just start working on something. force yourself to do art or build and eventually you'll get into it
3. put on a documentary, podcast, netflix show, or something like that while you work. it might make it more enjoyable
4. go try something new, or something you haven't done in awhile. sometimes when i get bored i'll reinstall an old steam game and try it out again.
5. similar to #1, social activities can help a lot with this sort of thing. after something social and a little stressful like Dungeons & Dragons or a good co-op game, or you know, actual human interaction, you'll enjoy being alone more.
6. turn those lights on. drink some caffeine. if you act like it's night you won't want to work as much.
7. clean up around your area. my work desk tends to go in cycles getting gradually more disgusting and crowded until i finally have enough (weekly?) and spend a really small amount of time (like 3-5 minutes) to clean it up. and once i get that done all the work feels a little better.
8. go outside and get some mild exercise. like walking your dogs or hiking to a nearby store
9. realize that it's okay to not do anything one day. that's the whole point of summer
10. Self Delete by stab
Hint: It's also known as relaxing
demotivation is not relaxing at all. it's quite frustrating, really