Over the last 2 weeks I went from 215 to 220 and the only significant change was a change in sleep habits, from a solid 8 to about 6 hours. Could sleep have that much of an impact?
It's possible. But sleep alone can't cause any weight gain. It is the increased appetite, due to hormone changes due to the lack of sleep which will cause the weight gain. Have you noticed such appetite changes?
There are a few ways you can gain weight: - Eating more kilo-joules then you burnt through exercise and metabolism - Having excess water retention (e.g. of a cause is protein deficiency) - Drinking excess water before weighing yourself - Pregnancy
Probably your weight gain is in water, unless your appetite has increased.
If you continue to gain weight without explanation, see a medical professional.
It's possible, although a 5lb weight gain in two weeks suggests that there might be other changes that are occurring that you are not considering.
Lack of sleep contributes to higher stress, usually caused by higher levels of cortisol in the system. Cortisol increases your appetite, and can change how your metabolism reacts, causing you to "hoard" the calories that you are taking in. Cortisol is usually highest in the mornings, tapering off during the day.
It's also been shown that the type of fat stored due to excess cortisol is the abdominal/visceral fat, which has a greater impact on heart and stroke related incidents.
Also, the hormones ghrelin (the "eat" stimulating hormone) and leptin (The "stop eating" signal hormone) are affected, causing you to have a greater appetite and to eat longer before stopping.
All of these can be factors in the weight gain cycle, and I would venture a guess that there is also some other stressor in your life that is causing you to miss the extra sleep. Adjust the external factors, and things should return to normal fairly soon.