Prescribed 100mg of prednisone day1 to taper off by 20mg until day6. is this safe, and considered long term use? afraid of bad side effects like weight gain, muscle loss,diabetes,etc.

Big dose.: You have been given a pretty big dose. 6 days is not considered long-term treatment. You may experience weight gain and be prone to changes in sugars. It all depends on why it was given to you. If it is for a really good reason, it can be a big help.

It is safe: No, a 6 day burst with taper like that is not consider long term use, and you shouldn't likely expect the long term repercussions of oral steroid use such as the ones you listed. You may feel like you have more energy, have a bigger appetite, and a little trouble sleeping, but that will only be short term and will dissipate quickly after finishing your 6 days, if you experience that at all.

OK: 6 days is not considered long-term and you should experience none of the long-term side effects that we worry about. You may have some of the short-term side effects - hungry, happy, hyper (some people it's more like hungry, angry, jittery).