When switching from lexapro (escitalopram) to zoloft is it common for their to be a down cycle, i.e depression, an how long should the transition take.?

Not necessarily: If your doctor is changing your medication, it may be because it wasn't serving your needs? Usually changes are made when people's symptoms don't respond, and better results are needed. I wouldn't expect there to be a "down cycle" unless Lexapro (escitalopram) was helping you more than you realized, and zoloft not so much -- or higher dose is needed. Please contact your prescribing doctor about this.

Not necessarily: As long as you take a dose of zoloft which is equivalent to the Lexapro (escitalopram) dose, the switch should be okay. Maybe you can discuss this with your prescribing physician as you shouldn't make adjustments on your own. Finally, and unlike lexapro, (escitalopram) zoloft may be better absorbed (you get more), when taken with food-perhaps up to 50% better absorbed with food. Good luck.