I've been on 1-1.5 hourly wake ups for the last 2 months since ours turned about 3.5 months. Before that he was sleeping through (8-9 hrs at a stretch!)
You just adjust to be honest. It's been tough sometimes but I think my body coped by dropping into deep sleep very quickly inbetween wake ups.
The first couple of weeks I felt a bit desperate but, once I let go of the hope of getting lovely long sleeps, it's not actually been as bad as it sounds.
Are you breast or bottle feeding?
I'm breastfeeding and since the sleep 'regression' we've been cosleeping (he was in side sleeper cot before). We set up a safe cosleeping position (no duvet or pillows near his head) and now, when he wakes I slide him over, feed then slide him back. Neither of us wake fully so it is not too disruptive.
I did consider sleep training but I thought I'd just try to ride it out and it now seems to be slowly getting better, in that I'm now getting one or two 2-3hr sleep sessions or night. The baby is 5.5 months old now so I'm hoping this is the start of an aural improvement.
No magic bullet to help I'm afraid. Just thought it may be helpful to share my experience. I'm lucky though as he will drop off v quickly after a feed so no extra rocking, winding etc which would definitely take a toll.
The last couple of months have not been sunshine and rainbows by any means and there have been many instances of 3am crying and swearing but weirdly I will miss the multiple nightly snuggles when he's sleeping better.
I'm sure you've already heard this but one theory is that the 4month regression is more accurately a progression from baby sleep patterns (basically they're either 'on or off') to a more adult sleep cycle (waking every 90 mins or so). The sleep regression is just them needing to work out how to link up the sleep cycles.
I expect there are theories on how you can get them to link cycles more quickly. I'll be v interested to read if sleep training or anything else has worked for others as we're not quite out of the woods ourselves yet!