Last year I was very sick and lost about 8kg and looked like an anorectic. After getting better I made it my intention to gain those 8kg back. It took about two months but I did it.
Here's what I did. I had firm faith that I will have my perfect weight again. I was very positive (It was easy to keep because I didn't want my family to worry) because I knew that I will achieve it, there is just no other way. When i started to see results, then it was even easier to keep that positive feeling. I didn't concentrate on what was at the moment - my skinny legs and ribs showing - I just concentrated on gaining those 8kg back. I think what made it easy was the knowing that gaining weight is easy. I didn't visualize I just concentrated on my perfect weight and felt happy knowing that i will have it.
What Bashar said: Circumstances don't matter, only state of being matters.