What are the medical problems during thunderstorms and lightning?

Storms: Medical problems depends on the individual patient. Psychologically speaking, storms can provoke anxiety in people, which we need to be aware of.

None: There are no medical conditions caused by thunderstorms and lightning. Unless of course you are hit by lightning, and then you might need to deal with severe burns and even death.

Same as fair weather: Fear and anxiety which are psychological and not pathological. The same as in fair weather.

Getting electrocuted: stay indoors, or if outdoors avoid standing under tall trees since they are more likely to be struck. If there is no shelter you may be better off lying flat, since lightning hits the highest point around, which if you are standing may be you. Dry off thoroughly as soon as you can, and wear rain resistant outer clothing. If you are in an area prone to this weather, follow reports and stay safe.

Asthma exacerbation: Agree with Dr Wartenberg's assessment but for those who have asthma, thunderstorm may cause an asthma attack as well.