The biggest key to recognising my hypos is a lack of need for sleep. If I'm just not tired or can't sleep cos of racing thoughts and needing to do something right away then I'm probably going hypo.
I do rein things in with sleeping tablets so that I have a soft landing and don't end up dipping into depression after a hypomania which is where the real problem lies for me. The hypomanias are not really that problematic but the depressions suck.