What causes low blood pressure and high pulse rate after exercising?

post exercise: Post exercise, the cardiac output drops fairly rapidly and the peripheral resistance less rapidly increases, this can cause lower BP and higher heart rate.

Dehydration.: This is why you need to hydrate yourself adequately before, during and after exercising. Especially if you are exercising in a hot environment. See if this improves with adequate hydration (water and/or electrolyte replenishment drinks). If not, then schedule a visit with a Cardiologist for an evaluation.