Just got back from paternity leave and feel like a ghost at work

Took 4 weeks off when my second was born and coming back to the office today. Everything changed while I was gone, new systems, new projects, different team structure. Plus I'm running on fumes because the baby has reflux and won't sleep longer than 45 minutes. How long did it take you guys to get back in the groove? Worried I'm gonna screw something up because my brain feels like pudding.