Horse
To see a horse in your dream, represents a strong, physical energy. You need to tame the wild forces. The dream may imply that you have been horsing around. Or perhaps you need to be less arrogant and "get off your high horse". If you see a dead horse in your dream, then it indicates that something in your life that initially offered you strength is now gone. This may refer to a relationship or situation.

To see a black or dark horse in your dream, signifies mystery, wildness, and the unknown. You may be taking a chance or gamble at some unknown area. It may even represents occult forces. If the horse is white, then it  signifies purity, prosperity and good fortunes. To dream that you are being chased by a white horse, may be a pun on chaste. Perhaps you are having difficulties dealing with issues of intimacy and sexuality.

To see a herd of wild horses in your dream, signifies a sense of freedom and lack of responsibilities/duties. Perhaps it may also indicated your uncontrolled emotions.

To dream that you are riding a horse, denotes that you will achieve success through underhanded means. You lack integrity. If you are riding a horse that is out of control, signifies that you are being carried away by your passions

Hmmm... I want to dream a white horses just after I purchase a lottery ticket      just wondering, thinking too much about it and 'causing' somehow to dream something (that white horse for example) could still mean good luck?

How about seeing a Unicorn??

aren't unicornes a symbol of eternal life?

No idea, & i think i saw a unicorn sometime ago, but don't remember if it was white/silver or balck, like the one in my avatar.