I have wound my dose of Sertraline (called Lustral here in the UK) up and down over the years 25/50/100/150 and have some experience of this. I have been on 50mg for about 3 years and decided to wind it down to 25mg (half tablet) before deciding to increase it up to 50mg again.
25>50mg I experience fatigue and tiredness, which usually abates after about 2 weeks. The anti-anxiety effects I experience after about 3 days and feel better, but sleep really heavy and need to sleep during the day for about 2 hrs. I usually just drink more coffee. I decided to increase my dose about 3 days before going on holiday for 1 week.
I always take my meds at 6pm each day.
If I had not been on meds for a while eg starting back on them after a couple of years, then I experience extreme fatigue for about 10 days. I would say that going straight on to 50mg is a bad idea, try 25mg until stable (about 3 weeks) then step up to 50mg, total time 6 weeks. IMHO this is the best way to do it.