Resistance in rear hub? I bought a new mid-range hybrid bike (Pinnacle Lithium), and for the first couple of weeks it was an absolute pleasure to ride. Then I went on holiday for two weeks, leaving it in a shed in the heat (if it's relevant). When I came back, it felt like the bike has slowed down. I'm pretty sure it did, because I have another bike that I still ride on the same set of gears, whereas with this one, I kind of went down from speed 6 to speed 3-4 at the back on the average ride. 

It feels like some mild, but noticeable resistance on both pedalling and the free ride. I've checked that the brakes don't touch the rims, re-lubricated the chain, made sure the tyre pressure is ok - the problem is still there. 

Could it be something like overtightened bearings in the rear hub or grease drying up there? Please tell me I'm not just imagining it :)
Hold the wheel off the ground. 

Spin it. 

See how quickly it slows down. 

Compare to the front wheel. If it's the same then "you're imagining it".

Make sure you have more than 50psi tyre pressure (20psi and it will feel like treacle)

Next time spend some of your holiday outside of bars and restaurants.