Don't worry, you wont get lymes from leaving a tick head in.
In fact you are better to get the tick out and leave the head in rather than leave the tick foe long enough to begin regurgitating. Ad long as when you remove the tick you don't squeeze the body or do anything else to cause it to regurgitate.
I pick up ticks daily. 365 days of the year, granted most days in the winter I only find single figures, but this time of year it can be endless, I have had 9 dug in today.
Catch them early, remove them properly and you have no worries from lymes. This powassan thing, I don't know. I hope i