What is the shortest time that a tan can fade? 10 points!?

I got this amazing natural tan not even a week ago and my tans usually last me a long time, even through some of winter if I am lucky! But I was just looking and my tan lines seem to be fading and my arms and chest don't seem to be as dark as they used to be. The thing is that I normally use aloe vera lotion, but I had misplaced it so I couldn't use it for an upwards of 4 days. I found it, but it was empty. Figures. I then found the same brand, Ocean Potion, in Aloe Gel and bought it. Aloe Vera Gel and Lotion are two different things, I understand that they are different and I want to know if they will preserve my tan to the same effect., and I really want to know if it was just the lighting/my eyes tricking me or can my tan fade that quickly??? Thanks!